Computer Organization

Transcription

1 Basics Machine, software, and program design JPC and JWD 2002 McGraw-Hill, Inc. Computer Organization CPU - central processing unit Where decisions are made, computations are performed, and input/output requests are delegated Memory Stores information being processed by the CPU Input devices Allows people to supply information to computers Output devices Allows people to receive information from computers 1

2 Computer Organization Memory Input Devices Output Devices CPU CPU Brains of the computer Arithmetic calculations are performed using the Arithmetic/Logical Unit or ALU Control unit decodes and executes instructions Arithmetic operations are performed using binary number system 2

3 Control Unit The fetch/execute cycle is the steps the CPU takes to execute an instruction Performing the action specified by an instruction is known as executing the instruction The program counter (PC) holds the memory address of the next instruction Fetch the instruction to which the PC points Increment the PC Execute the fetched instruction Input and Output Devices Accessories that allow computer to perform specific tasks Receive information for processing Return the results of processing Store information Common input and output devices Speakers Mouse Scanner Printer Joystick CD-ROM Keyboard Microphone DVD Some devices are capable of both input and output Floppy drive Hard drive Magnetic tape units 3

4 Monitor Display device that operates like a television Also known as CRT (cathode ray tube) Controlled by an output device called a graphics card Displayable area Measured in dots per inch, dots are often referred to as pixels (short for picture element) Standard resolution is 640 by 480 Many cards support resolution of 1280 by 1024 or better 1280 pixels across screen Number of colors supported varies from 16 to billions 1024 pixels down screen Software Application software Programs designed to perform specific tasks that are transparent to the user System software Programs that support the execution and development of other programs Two major types Operating systems Translation systems 4

5 Application Software Application software is the software that has made using computers indispensable and popular Common application software Word processors Desktop publishing programs Spreadsheets Presentation managers Drawing programs Learning how to develop application software is our focus Operating System Examples Windows, UNIX, Mac OS X Controls and manages the computing resources Important services that an operating system provides File system Directories, folders, files Commands that allow for manipulation of the file system Sort, delete, copy Ability to perform input and output on a variety of devices Management of the running systems 5

6 Translation System Set of programs used to develop software A key component of a translation system is a translator Some types of translators Compiler Converts from one language to another Linker Examples Combines resources Microsoft Visual C++, CBuilder, g++, Code Warrior Performs compilation, linking, and other activities. Software Development Activities Editing Compiling Linking with precompiled files Object files Library modules Loading and executing Viewing the behavior of the program 6

7 Software Development Cycle Source Program Compile Edit Think Link Load Library routines Other object files Execute IDEs Integrated Development Environments or IDEs Supports the entire software development cycle E.g., MS Visual C++, Borland, Code Warrior Provides all the capabilities for developing software Editor Compiler Linker Loader Debugger Viewer 7

8 Engineering Software Software engineering Area of computer science concerned with building large software systems Challenge Tremendous advances in hardware have not been accompanied by comparable advances in software Complexity Trade-off System complexity tends to grow as the system becomes more user friendly High Complexity Total Software Complexity User Simplicity Low 8

9 Software Engineering Goals Reliability An unreliable life-critical system can be fatal Understandability Future development is difficult if software is hard to understand Cost Effectiveness Cost to develop and maintain should not exceed profit Adaptability System that is adaptive is easier to alter and expand Reusability Improves reliability, maintainability, and profitability Software Engineering Principles Abstraction Extract the relevant properties while ignoring inessentials Encapsulation Hide and protect essential information through a controlled interface Modularity Dividing an object into smaller modules so that it is easier to understand and manipulate Hierarchy Ranking or ordering of objects based on some relationship between them 9

10 Abstraction Extract the relevant object properties while ignoring inessentials Defines a view of the object Example - car Car dealer views a car from selling features standpoint Price, length of warranty, color, Mechanic views a car from systems maintenance standpoint Size of the oil filter, type of spark plugs, Price? Oil change? Encapsulation Steps Decompose an object into parts Hide and protect essential information Supply interface that allows information to be modified in a controlled and useful manner Internal representation can be changed without affecting other system parts Example - car radio Interface consists of controls and power and antenna connectors The details of how it works is hidden To install and use a radio Do not need to know anything about the radio s electronics 10

11 Modularity Dividing an object into smaller pieces or modules so that the object is easier to understand and manipulate Most complex systems are modular Example - Automobile can be decomposed into subsystems Cooling system Radiator Thermostat Water pump Ignition system Battery Starter Spark plugs Hierarchy Hierarchy Ranking or ordering of objects based on some relationship between them Help us understand complex systems Example - a company hierarchy helps employees understand the company and their positions within it For complex systems, a useful way of ordering similar abstractions is a taxonomy from least general to most general 11

12 Northern Timber Wolf Taxonomy Kingdom Animalia Phylum Chordata Class Mammalia Order Carnivora Family Caninae Genus Canis Species Canis lupus Subspecies Canis lupus occidentalis Northern Timber Wolf OO Design and Programming Object-oriented design and programming methodology supports good software engineering Promotes thinking in a way that models the way we think and interact with the real world Example - watching television The remote is a physical object with properties Weight, size, can send message to the television The television is also a physical object with various properties 12

13 Objects An object is almost anything with the following characteristics Name Properties The ability to act upon receiving a message Basic message types Directive to perform an action Request to change one of its properties Binary Arithmetic The individual digits of a binary number are referred to as bits Each bit represents a power of two = = = = 2 Binary addition Equivalent decimal addition 13

14 Binary Arithmetic Binary multiplication Equivalent decimal multiplication Two s Complement Representation for signed binary numbers Leading bit is a sign bit Binary number with leading 0 is positive Binary number with leading 1 is negative Magnitude of positive numbers is just the binary representation Magnitude of negative numbers is found by Complement the bits Replace all the 1's with 0's, and all the 0's with 1's Add one to the complemented number The carry in the most significant bit position is thrown away when performing arithmetic 14

15 Two s Complement Performing two's complement on the decimal 7 to get -7 Using a five-bit representation 7 = Convert to binary Complement the bits Add 1 to the complement Result is -7 in two's complement Two's Complement Arithmetic Computing 8-7 using a two's complement representation with five-bit numbers 8-7 = 8 + (-7) = Two's complement of 8 Throw away the high-order carry as we are using a five bit representation Two's complement of Add 8 and Is the five-bit result 15

16 Fundamentals of C++ Basic programming elements and concepts JPC and JWD 2002 McGraw-Hill, Inc. Program Organization Program statement Definition Declaration Action Executable unit Named set of program statements Different languages refer to executable units by different names Subroutine: Fortran and Basic Procedure: Pascal Function : C++ 16

17 Program Organization C++ program Collection of definitions, declarations and functions Collection can span multiple files Advantages Structured into small understandable units Complexity is reduced Overall program size decreases Object Object is a representation of some information Name Values or properties Data members Ability to react to requests (messages)!! Member functions When an object receives a message, one of two actions are performed Object is directed to perform an action Object changes one of its properties 17

18 A First Program - Greeting.cpp Preprocessor directives Function named main() indicates start of program // Program: Display greetings // Author(s): Ima Programmer // Date: 1/24/2001 Comments #include <iostream> #include <string> Provides simple access using namespace std; int main() { cout << "Hello world!" << endl; return 0; Ends executions of main() which ends program Insertion statement Function Greeting Output 18

19 #include <iostream> using namespace std; int main() { // Extract length and width cout << "Rectangle dimensions: "; float Length; float Width; cin >> Length >> Width; Area.cpp Definitions Extraction // Compute and insert the area float Area = Length * Width; Definition with initialization cout << "Area = " << Area << " = Length " << Length << " * Width " << Width << endl; return 0; Visual C++ IDE with Area.cpp 19

20 Area.cpp Output Comments Allow prose or commentary to be included in program Importance Programs are read far more often than they are written Programs need to be understood so that they can be maintained C++ has two conventions for comments // single line comment (preferred) /* long comment */ (save for debugging) Typical uses Identify program and who wrote it Record when program was written Add descriptions of modifications 20

21 Fundamental C++ Objects C++ has a large number of fundamental or built-in object types The fundamental object types fall into one of three categories Integer objects Floating-point objects Character objects P Z 3.14 Integer Object Types The basic integer object type is int The size of an int depends on the machine and the compiler On PCs it is normally 16 or 32 bits Other integers object types short: typically uses less bits long: typically uses more bits Different types allow programmers to use resources more efficiently Standard arithmetic and relational operations are available for these types 21

22 Integer Constants Integer constants are positive or negative whole numbers Integer constant forms Decimal Octal (base 8) Digits 0, 1, 2, 3, 4, 5, 6, 7 Hexadecimal (base 16) Digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, A, B, C, D, E, F Consider 31 oct and 25 dec Decimal Constants Examples L L or l indicates long integer 23a (illegal) The type of the constant depends on its size, unless the type specifier is used 22

23 Character Object Types Character type char is related to the integer types Characters are encoded using a scheme where an integer represents a particular character ASCII is the dominant encoding scheme Examples ' ' encoded as 32 '+' encoded as 43 'A' encoded as 65 'Z' encoded as 90 'a' encoded as 97 'z' encoded as 122 Appendix A gives the complete ASCII character set Character Operations Arithmetic and relational operations are defined for characters types 'a' < 'b' is true '4' > '3' is true '6' <= '2' is false 23

24 Character Constants Explicit (literal) characters within single quotes 'a','d','*' Special characters - delineated by a backslash \ Two character sequences (escape codes) Some important special escape codes \t denotes a tab \n denotes a new line \\ denotes a backslash \' denotes a single quote \" denotes a double quote '\t' is the explicit tab character, '\n' is the explicit new line character, and so on Literal String Constants A literal string constant is a sequence of zero or more characters enclosed in double quotes "We are even loonier than you think" "Rust never sleeps\n" "Nilla is a Labrador Retriever" Not a fundamental type 24

25 Floating-Point Object Types Floating-point object types represent real numbers Integer part Fractional part The number breaks down into the following parts integer part fractional part C++ provides three floating-point object types float double long double Floating-Point Constants Standard decimal notation F F or f indicates single precision floating point value Standard scientific notation 1.45E e-3L L or l indicates long double floating point value When not specified, floating-point constants are of type double 25

26 Names Used to denote program values or components A valid name is a sequence of Letters (upper and lowercase) Digits A name cannot start with a digit Underscores A name should not normally start with an underscore Names are case sensitive MyObject is a different name than MYOBJECT There are two kinds of names Keywords Identifiers Keywords Keywords are words reserved as part of the language int, return, float, double They cannot be used by the programmer to name things They consist of lowercase letters only They have special meaning to the compiler 26

27 Identifiers Identifiers should be Short enough to be reasonable to type (single word is norm) Standard abbreviations are fine (but only standard abbreviations) Long enough to be understandable When using multiple word identifiers capitalize the first letter of each word Examples Min Temperature CameraAngle CurrentNbrPoints Definitions All objects that are used in a program must be defined An object definition specifies Type Name General definition form Known type List of one or more identifiers Type Id, Id,..., Id; Our convention is one definition per statement! 27

28 Examples char Response; int MinElement; float Score; float Temperature; int i; int n; char c; float x; Objects are uninitialized with this definition form (Value of a object is whatever is in its assigned memory location) Arithmetic Operators Common Addition + Subtraction - Multiplication * Division / Mod % Note No exponentiation operator Single division operator Write m*x + b not mx + b Operators are overloaded to work with more than one type of object 28

29 Integer Division Integer division produces an integer result Truncates the result Examples 3 / 2 evaluates to 1 4 / 6 evaluates to 0 10 / 3 evaluates to 3 Mod Produces the remainder of the division Examples 5 % 2 evaluates to 1 12 % 4 evaluates to 0 4 % 5 evaluates to 4 29

30 Operators and Precedence Consider mx + b Consider m*x + b which of the following is it equivalent to (m * x) + b m * (x + b) Operator precedence tells how to evaluate expressions Standard precedence order () Evaluate first, if nested innermost done first * / % Evaluate second. If there are several, then evaluate from left-to-right + - Evaluate third. If there are several, then evaluate from left-to-right Operator Precedence Examples 20-4 / 5 * * 5 % 4 (4 / 5) ((4 / 5) * 2) ((4 / 5) * 2) (3 * 5) ((4 / 5) * 2) ((3 * 5) % 4) (20 -((4 / 5) * 2)) ((3 * 5) % 4) (20 -((4 / 5) * 2)) + ((3 * 5) % 4) 30

31 Defining and Initializing When an object is defined using the basic form, the memory allotted to it contains random information Better idea to specify its desired value at the same time Exception is when the next statement is an extraction for the object Remember our convention of one definition per statement! Examples int FahrenheitFreezing = 32; char FinalGrade = 'A'; cout << "Slope of line: "; float m; cin >> m; cout << "Intercept: "; float b; cin >> b; cout << "X value of interest: "; float x; cin >> x; float y = (m * x) + b; 31

32 Modifying Objects Operators and Expressions JPC and JWD 2002 McGraw-Hill, Inc. Memory Depiction float y = 12.5; y

33 Memory Depiction float y = 12.5; int Temperature = 32; y Temperature Memory Depiction float y = 12.5; int Temperature = 32; char Letter = 'c'; y Temperature Letter 'c'

34 Memory Depiction float y = 12.5; int Temperature = 32; char Letter = 'c'; int Number; y Temperature Letter Number 'c' Assignment Statement Basic form object = expression ; Target becomes source Celsius = (Fahrenheit - 32) * 5 / 9; y = m * x + b; Action Expression is evaluated Expression value stored in object 34

35 Definition int NewStudents = 6; NewStudents 6 Definition int NewStudents = 6; int OldStudents = 21; NewStudents OldStudents

36 Definition int NewStudents = 6; int OldStudents = 21; int TotalStudents; NewStudents OldStudents TotalStudents Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; NewStudents OldStudents TotalStudents 6 21? TotalStudents = NewStudents + OldStudents; 36

37 Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; NewStudents OldStudents TotalStudents TotalStudents = NewStudents + OldStudents; Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; NewStudents OldStudents TotalStudents 6? 27 TotalStudents = NewStudents + OldStudents; OldStudents = TotalStudents; 37

38 Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; NewStudents OldStudents TotalStudents TotalStudents = NewStudents + OldStudents; OldStudents = TotalStudents; Consider int Value1 = 10; Value

39 Consider int Value1 = 10; int Value2 = 20; Value1 Value Consider int Value1 = 10; int Value2 = 20; int Hold = Value1; Value1 Value2 Hold

40 Consider int Value1 = 10; int Value2 = 20; int Hold = Value1; Value1 = Value2; Value1 Value2 Hold? Consider int Value1 = 10; int Value2 = 20; int Hold = Value1; Value1 = Value2; Value1 Value2 Hold

41 Consider int Value1 = 10; int Value2 = 20; int Hold = Value1; Value1 = Value2; Value1 Value2 Hold 20? 10 Value2 = Hold; Consider int Value1 = 10; int Value2 = 20; int Hold = Value1; Value1 = Value2; Value1 Value2 Hold Value2 = Hold; We swapped the values of objects Value1 and Value2 using Hold as temporary holder for Value1 s starting value! 41

42 Incrementing int i = 1; i 1 Incrementing int i = 1; i 1 i = i + 1; i 2 Assign the value of expression i + 1 to i Evaluates to 2 42

43 Const Definitions Modifier const indicates that an object cannot be changed Object is read-only Useful when defining objects representing physical and mathematical constants const float Pi = ; Value has a name that can be used throughout the program const int SampleSize = 100; Makes changing the constant easy Only need to change the definition and recompile Assignment Conversions Floating-point expression assigned to an integer object is truncated Integer expression assigned to a floating-point object is converted to a floating-point value Consider float y = 2.7; int i = 15; int j = 10; i = y; // i is now 2 cout << i << endl; y = j; // y is now 10.0 cout << y << endl; 43

44 Nonfundamental Types Nonfundamental as they are additions to the language C++ permits definition of new types and classes A class is a special kind of type Class objects typically have Data members that represent attributes and values Member functions for object inspection and manipulation Members are accessed using the selection operator (.) j = s.size(); Auxiliary functions for other behaviors Libraries often provide special-purpose types and classes Programmers can also define their own types and classes Examples Standard Template Library (STL) provides class string EzWindows library provides several graphical types and classes SimpleWindow is a class for creating and manipulating window objects RectangleShape is a class for creating and manipulating rectangle objects 44

45 Class string Class string Used to represent a sequence of characters as a single object Some definitions string Name = "Joanne"; string DecimalPoint = "."; string empty = ""; string copy = name; string Question = '?'; // illegal Nonfundamental Types To access a library use a preprocessor directive to add its definitions to your program file #include <string> The using statement makes syntax less clumsy Without it std::string s = "Sharp"; std::string t = "Spiffy"; With it using namespace std; // std contains string string s = "Sharp"; string t = "Spiffy"; 45

46 EzWindows Library Objects Definitions are the same form as other objects Example SimpleWindow W; Most non-fundamental classes have been created so that an object is automatically initialized to a sensible value SimpleWindow objects have member functions to process messages to manipulate the objects Most important member function is Open() which causes the object to be displayed on the screen Example W.Open(); Initialization Class objects may have several attributes to initialize Syntax for initializing an object with multiple attributes Type Identifier(Exp 1, Exp 2,..., Exp n ); SimpleWindow object has several optional attributes SimpleWindow W("Window Fun", 8, 4); First attribute Window banner Second attribute Width of window in centimeters Third attribute Height of window in centimeters 46

47 An EzWindows Program #include <iostream> using namespace std; #include "ezwin.h" int ApiMain() { SimpleWindow W("A Window", 12, 12); W.Open(); cout << "Enter a character to exit" << endl; char a; cin >> a; return 0; An EzWindows Project File 47

48 An EzWindows Project File Sample Display Behavior 48

49 RectangleShape Objects EzWindows also provides RectangleShape for manipulating rectangles RectangleShape objects can specify the following attributes SimpleWindow object that contains the rectangle (mandatory) Offset from left edge of the SimpleWindow Offset from top edge of the SimpleWindow Offsets are measured in centimeters from rectangle center Width in centimeters Height in centimeters Color color is an EzWindows type RectangleShape Objects Examples SimpleWindow W1("My Window", 20, 20); SimpleWindow W2("My Other Window", 15, 10); RectangleShape R(W1, 4, 2, Blue, 3, 2); RectangleShape S(W2, 5, 2, Red, 1, 1); RectangleShape T(W1, 3, 1, Black, 4, 5); RectangleShape U(W1, 4, 9); 49

50 RectangleShape Objects Some RectangleShape member functions for processing messages Draw() Causes rectangle to be displayed in its associated window GetWidth() Returns width of object in centimeters GetHeight() Returns height of object in centimeters SetSize() Takes two attributes -- a width and height -- that are used to reset dimensions of the rectangle Another EzWindows Program #include <iostream> using namespace std; #include "rect.h" int ApiMain() { SimpleWindow W("Rectangular Fun", 12, 12); W.Open(); RectangleShape R(W, 5.0, 2.5, Blue, 1, 2); R.Draw(); cout << "Enter a character to exit" << endl; char Response; cin >> Response; return 0; 50

51 Sample Display Behavior Compound Assignment C++ has a large set of operators for applying an operation to an object and then storing the result back into the object Examples int i = 3; i += 4; // i is now 7 cout << i << endl; float a = 3.2; a *= 2.0; // a is now 6.4 cout << a << endl; 51

52 Increment and Decrement C++ has special operators for incrementing or decrementing an object by one Examples int k = 4; ++k; // k is 5 k++; // k is 6 cout << k << endl; int i = k++; // i is 6, k is 7 cout << i << " " << k << endl; int j = ++k; // j is 8, k is 8 cout << j << " " << k << endl; Class string Some string member functions size() determines number of characters in the string string Saying = "Rambling with Gambling"; cout << Saying.size() << endl; // 22 substr() determines a substring (Note first position has index 0) string Word = Saying.substr(9, 4); // with find() computes the position of a subsequence int j = Saying.find("it"); // 10 int k = Saying.find("its"); //? 52

53 Class string Auxiliary functions and operators getline() extracts the next input line string Response; cout << "Enter text: "; getline(cin, Response, '\n'); cout << "Response is \"" << Response << "\" << endl; Example run Enter text: Want what you do Response is "Want what you do" Class string Auxiliary operators + string concatenation string Part1 = "Me"; string Part2 = " and "; string Part3 = "You"; string All = Part1 + Part2 + Part3; += compound concatenation assignment string ThePlace = "Brooklyn"; ThePlace += ", NY"; 53

54 #include <iostream> using namespace std; int main() { cout << "Enter the date in American format: " << "(e.g., January 1, 2001) : "; string Date; getline(cin, Date, '\n'); int i = Date.find(" "); string Month = Date.substr(0, i); int k = Date.find(","); string Day = Date.substr(i + 1, k - i - 1); string Year = Date.substr(k + 2, Date.size() - 1); string NewDate = Day + " " + Month + " " + Year; cout << "Original date: " << Date << endl; cout << "Converted date: " << NewDate << endl; return 0; 54

55 If Control Construct A mechanism for deciding whether an action should be taken JPC and JWD 2002 McGraw-Hill, Inc. Boolean Algebra Logical expressions have the one of two values - true or false A rectangle has three sides The instructor has a pleasant smile The branch of mathematics is called Boolean algebra Developed by the British mathematician George Boole in the 19th century Three key logical operators And Or Not 55

56 Boolean Algebra Truth tables Lists all combinations of operand values and the result of the operation for each combination Example P Q P and Q False False False False True False True False False True True True Boolean Algebra Or truth table P Q P or Q False False False False True True True False True True True True 56

57 Boolean Algebra Not truth table P False True not P True False Boolean Algebra Can create complex logical expressions by combining simple logical expressions Example not (P and Q) A truth table can be used to determine when a logical expression is true P Q P and Q not (P and Q) False False False True False True False True True False False True True True True False 57

58 A Boolean Type C++ contains a type named bool Type bool has two symbolic constants true false Boolean operators The and operator is && The or operator is The not operator is! Warning & and are also operators so be careful what you type A Boolean Type Example logical expressions bool P = true; bool Q = false; bool R = true; bool S = (P && Q); bool T = ((!Q) R); bool U =!(R && (!Q)); 58

59 Relational Operators Equality operators ==!= Examples int i = 32; int k = 45; bool q = (i == k); bool r = (i!= k); Relational Operators Ordering operators < > >= <= Examples int i = 5; int k = 12; bool p = (i < 10); bool q = (k > i); bool r = (i >= k); bool s = (k <= 12); 59

60 Operator Precedence Revisited Precedence of operators (from highest to lowest) Parentheses Unary operators Multiplicative operators Additive operators Relational ordering Relational equality Logical and Logical or Assignment Operator Precedence Revisited Consider 5 * == 13 && 12 < 19!false == 5 < 24 60

61 Operator Precedence Revisited Consider 5 * == 13 && 12 < 19!false == 5 < 24 Yuck! Do not write expressions like this! Operator Precedence Revisited Consider 5 * == 13 && 12 < 19!false == 5 < 24 However, for your information it is equivalent to ((((5 *15) + 4) == 13) && (12 < 19)) ((!false) == (5 < 24)) 61

62 Conditional Constructs Provide Ability to control whether a statement list is executed Two constructs If statement if if-else if-else-ef Switch statement Left for reading The Basic If Statement Syntax if (Expression) Action If the Expression is true then execute Action Action is either a single statement or a group of statements within braces Expression true Action false 62

63 Example if (Value < 0) { Value = -Value; Is our number negative? If Value is less than zero then we need to update its value to that of its additive inverse Value < 0 true Value = -Value false If Value is not less than zero then our number is fine as is Our number is now definitely nonnegative Sorting Two Numbers cout << "Enter two integers: "; int Value1; int Value2; cin >> Value1 >> Value2; if (Value1 > Value2) { int RememberValue1 = Value1; Value1 = Value2; Value2 = RememberValue1; cout << "The input in sorted order: " << Value1 << " " << Value2 << endl; 63

64 Semantics Rearrange value1 and value2 to put their values in the proper order value2 < value1 true Are the numbers out of order false int remembervalue1 = value1 value1 = value2 value2 = remembervalue1 The numbers were rearranged into the proper order The numbers are in order The numbers were initially in order What is the Output? int m = 5; int n = 10; if (m < n) ++m; ++n; cout << " m = " << m << " n = " n << endl; 64

65 The If-Else Statement Syntax if (Expression) Action 1 else Action 2 If Expression is true then execute Action 1 otherwise execute Action 2 if (v == 0) { cout << "v is 0"; else { cout << "v is not 0"; Expression true false Action 1 Action 2 Finding the Max cout << "Enter two integers: "; int Value1; int Value2; cin >> Value1 >> Value2; int Max; if (Value1 < Value2) { Max = Value2; else { Max = Value1; cout << "Maximum of inputs is: " << Max << endl; 65

66 Finding the Max Is Value2 larger than Value1 Yes, it is. So Value2 is larger than Value1. In this case, Max is set to Value2 true Value1 < Value2 false No, its not. So Value1 is at least as large as Value2. In this case, Max is set to Value1 Max = Value2 Max = Value1 Either case, Max is set correctly Selection It is often the case that depending upon the value of an expression we want to perform a particular action Two major ways of accomplishing this choice if-else-if statement if-else statements glued together Switch statement An advanced construct 66

67 An If-Else-If Statement if ( nbr < 0 ){ cout << nbr << " is negative" << endl; else if ( nbr > 0 ) { cout << nbr << " is positive" << endl; else { cout << nbr << " is zero" << endl; A Switch Statement switch (ch) { case 'a': case 'A': case 'e': case 'E': case 'i': case 'I': case 'o': case 'O': case 'u': case 'U': cout << ch << " is a vowel" << endl; break; default: cout << ch << " is not a vowel" << endl; 67

68 cout << "Enter simple expression: "; int Left; int Right; char Operator; cin >> Left >> Operator >> Right; cout << Left << " " << Operator << " " << Right << " = "; switch (Operator) { case '+' : cout << Left + Right << endl; break; case '-' : cout << Left - Right << endl; break; case '*' : cout << Left * Right << endl; break; case '/' : cout << Left / Right << endl; break; default: cout << "Illegal operation" << endl; 68

69 Iterative Constructs Mechanisms for deciding under what conditions an action should be repeated JPC and JWD 2002 McGraw-Hill, Inc. Averaging 69

70 Determining Average Magnitude Suppose we want to calculate the average apparent brightness of a list of five star magnitude values Can we do it? Yes, it would be easy Suppose we want to calculate the average apparent brightness of a list of 8,479 stars visible from earth Can we do it Yes, but it would be gruesome without the use of iteration C++ Iterative Constructs Three constructs while statement for statement do-while statement 70

71 While Syntax Logical expression that determines whether the action is to be executed Action to be iteratively performed until logical expression is false while ( Expression ) Action While Semantics Expression is evaluated at the start of each iteration of the loop Expression If Expression is true, Action is executed true Action false If Expression is false, program execution continues with next statement 71

72 Computing an Average int listsize = 4; int numberprocessed = 0; double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize 4 int listsize = 4; int numberprocessed = 0; double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; 72

73 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; int numberprocessed = 0; double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; 4 0 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

74 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

75 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

76 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

77 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

78 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

79 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

80 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

81 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

82 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

83 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

84 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; value double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum 10 int numberprocessed = 0; average 2.5 double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl;

85 Execution Trace Suppose input contains: listsize numberprocessed int listsize = 4; sum int numberprocessed = 0; average double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; Execution Trace Suppose input contains: Stays in stream until extracted int listsize = 4; int numberprocessed = 0; double sum = 0; while (numberprocessed < listsize) { double value; cin >> value; sum += value; ++numberprocessed; double average = sum / numberprocessed ; cout << "Average: " << average << endl; 85

86 Power of Two Table const int TableSize = 20; int i = 0; long Entry = 1; cout << "i" << "\t\t" << "2 ** i" << endl; while (i < TableSize) { cout << i << "\t\t" << Entry << endl; Entry = 2 * Entry; ++i; Better Way of Averaging int numberprocessed = 0; The value of the input double sum = 0; operation corresponds to true only if a successful double value; extraction was made while ( cin >> value ) { sum += value; What if list is ++numberprocessed; empty? double average = sum / numberprocessed ; cout << "Average: " << average << endl; 86

87 Even Better Way of Averaging int numberprocessed = 0; double sum = 0; double value; while ( cin >> value ) { sum += value; ++numberprocessed; if ( numberprocessed > 0 ) { double average = sum / numberprocessed ; cout << "Average: " << average << endl; else { cout << "No list to average" << endl; The For Statement Syntax for (ForInit ; ForExpression; PostExpression) Action Example for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; 87

88 Evaluated once at the beginning of the for statements's execution If ForExpr is true, Action is executed ForInit ForExpr true false The ForExpr is evaluated at the start of each iteration of the loop After the Action has completed, the PostExpression is evaluated Action If ForExpr is false, program execution continues with next statement PostExpr After evaluating the PostExpression, the next iteration of the loop starts Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 0 88

89 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 0 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 0 i is 0 89

90 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 0 i is 0 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 1 i is 0 90

91 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 1 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 1 i is 0 i is 1 91

92 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 1 i is 0 i is 1 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 2 i is 0 i is 1 92

93 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 2 i is 0 i is 1 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 2 i is 0 i is 1 i is 2 93

94 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 2 i is 0 i is 1 i is 2 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 3 i is 0 i is 1 i is 2 94

95 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 3 i is 0 i is 1 i is 2 Execution Trace for (int i = 0; i < 3; ++i) { cout << "i is " << i << endl; cout << "all done" << endl; i 3 i is 0 i is 1 i is 2 all done 95

96 Table Revisiting const int TableSize = 20; long Entry = 1; cout << "i" << "\t\t" << "2**i" << endl; for (int i = 0; i <= TableSize; ++i) { cout << i << "\t\t" << Entry << endl; Entry *= 2; Table Revisiting const int TableSize = 20; long Entry = 1; cout << "i" << "\t\t" << "2**i" << endl; for (int i = 0; i < TableSize; ++i) { cout << i << "\t\t" << Entry << endl; Entry = 2 * Entry; cout << "i is" << i << endl; // illegal The scope of i is limited to the loop! 96

97 Displaying a Diagonal SimpleWindow W("One diagonal", 5.5, 2.25); W.Open(); for (int j = 1; j <= 3; ++j) { float x = j * ; float y = j * ; float Side = 0.4; RectangleShape S(W, x, y, Blue, Side, Side); S.Draw(); Sample Display 97

98 Displaying Three Diagonals SimpleWindow W("Three diagonals", 6.5, 2.25); W.Open(); for (int i = 1; i <= 3; ++i) { for (int j = 1; j <= 3; ++j) { float x = i j * ; float y = j * ; float Side = 0.4; RectangleShape S(W, x, y, Blue, Side, Side); S.Draw(); The scope of i includes the inner loop. The scope of j is just the inner loop. Sample Display 98

99 int Counter1 = 0; int Counter2 = 0; int Counter3 = 0; int Counter4 = 0; int Counter5 = 0; ++Counter1; for (int i = 1; i <= 10; ++i) { ++Counter2; for (int j = 1; j <= 20; ++j) { ++Counter3; ++Counter4; ++Counter5; cout << Counter1 << " " << Counter2 << " " << Counter3 << " " << Counter4 << " " << Counter5 << endl; For Into While Observation The for statement is equivalent to { ForInit; while (ForExpression) { Action; PostExpression; 99

100 Counting Characters int NumberOfNonBlanks = 0; int NumberOfUpperCase = 0; char c; Only extracts while (cin >> c) { nonblank characters ++NumberOfNonBlanks; if ((c >= 'A') && (c <= 'Z')) { ++NumberOfUpperCase; cout << "Nonblank characters: " << NumberOfNonBlanks << endl << "Uppercase characters: " << NumberOfUpperCase << endl; Counting All Characters char c; int NumberOfCharacters = 0; int NumberOfLines = 0; while ( cin.get(c) ) { ++NumberOfCharacters; if (c == '\n') { ++NumberOfLines Extracts all characters cout << "Characters: " << NumberOfCharacters << endl << "Lines: " << NumberOfLines << endl; 100

101 #include <iostream> #include <fstream> File Processing using namespace std; int main() { ifstream fin("mydata.txt"); int ValuesProcessed = 0; float ValueSum = 0; float Value; while ( fin >> Value ) { ValueSum += Value; ++ValuesProcessed; if (ValuesProcessed > 0) { ofstream fout("average.txt"); float Average = ValueSum / ValuesProcessed; fout << "Average: " << Average << endl; return 0; else { cerr << "No list to average" << endl; return 1; Iteration Do s Key Points Make sure there is a statement that will eventually terminate the iteration criterion The loop must stop! Make sure that initialization of loop counters or iterators is properly performed Have a clear purpose for the loop Document the purpose of the loop Document how the body of the loop advances the purpose of the loop 101

102 The Do-While Statement Syntax do Action while (Expression) Semantics Execute Action If Expression is true then execute Action again Repeat this process until Expression evaluates to false Action is either a single statement or a group of statements within braces Action Expression false true Waiting for a Proper Reply char Reply; do { cout << "Decision (y, n): "; if (cin >> Reply) Reply = tolower(reply); else Reply = 'n'; while ((Reply!= 'y') && (Reply!= 'n')); 102

103 Libraries Computational assistants JPC and JWD 2002 McGraw-Hill, Inc. Functions Previous examples Programmer-defined functions main() ApiMain() Library-defined functions cin.get() Advice string member functions size() RectangleShape member function Draw() SimpleWindow member function Open() Don t reinvent the wheel! There are lots of libraries out there 103

104 Terminology A function is invoked by a function call / function invocation y = f(a); Terminology A function call specifies The function name The name indicates what function is to be called y = f(a); The actual parameters to be used in the invocation The values are the information that the called function requires from the invoking function to do its task y = f(a); 104

105 Terminology A function call produces a return value The return value is the value of the function call y = f(a); Invocation Process Flow of control is temporarily transferred to the invoked function Correspondence established between actual parameters of the invocation with the formal parameters of the definition cout << "Enter number: "; double a; cin >> a; y = f(a); cout << y; double f(double x) { double result = x*x + 2*x + 5; Value of a is given to x return result; 105

106 Invocation Process Flow of control is temporarily transferred to the invoked function Local objects are also maintained in the invocation s activation record. Even main() has a record cout << "Enter number: "; double a; cin >> a; double f(double x) { y = f(a); double result = cout << y; x*x + 2*x + 5; Activation record is large enough to store values return result; associated with each object that is defined by the function Invocation Process Flow of control is temporarily transferred to the invoked function Other information may also be maintained in the invocation s activation record cout << "Enter number: "; double a; cin >> a; double f(double x) { y = f(a); double result = cout << y; x*x + 2*x + 5; Possibly a pointer to the current statement being return result; executed and a pointer to the invoking statement 106

107 Invocation Process Flow of control is temporarily transferred to the invoked function Next statement executed is the first one in the invoked function cout << "Enter number: "; double a; double f(double x) { cin >> a; double result = y = f(a); cout << y; x*x + 2*x + 5; return result; Invocation Process Flow of control is temporarily transferred to the invoked function After function completes its action, flow of control is returned to the invoking function and the return value is used as value of invocation cout << "Enter number: "; double a; double f(double x) { cin >> a; double result = y = f(a); cout << y; x*x + 2*x + 5; return result; 107