Instructor : Stan Kong

Transcription

1 ET2560 Introduction to C Programming Mid Term Review Instructor : Stan Kong skong@itt tech.edutech.edu

2 Computers and Programs Computer A machine that processes data under the control of a stored program Requires hardware, software, and data Program A series of instructions that guide a computer through a process

3 Figure 1.3 Components of a Computer

4 Central Processing Unit Central Processing Unit (CPU) has tworoles: coordinating all computer operations and performing arithmetic and logical operations on data.

5 Main Memory Main memorystores programs, data and results. Most computers have two types of main memory: random access memory (RAM) and read only memory (ROM). RAM which offer temporary storage of program and data. RAM is usually volatile memory, which means that everything in RAM will be lost when the computer is switched off. ROM which stores programs or data permanently, it is not volatile. Thecomputer can read, but cannot write information in ROM.

6 Secondary Storage Devices Computer systems provide storage in addition to main memory for two reason. First, computers need storage that is permanent so that information can be retained during a power loss of when computer is turn off. Second, systems typically store more information than will fit in memory.

7 Input/Output Devices Input/output devices are use to communicate with the computer. Specifically they allow us to enter data for a computation and to observe the results of that computation. For example, keyboard is an input device and a monitor is an output device.

8 The operating system is a set of system software routines that interface between an application program and the hardware. It is responsible to manage processor resource and memory resource and load program into memory. User Application program Operating system Computer Hardware

9 Machine languages are the only languages understood by computers. While easily understood by computers, machine languages are almost impossible for humans to use because they consist it entirely of numbers. A compiler converts each source statement to one or more machine level instructions (machine languages). Library Linker Executable Program

10 Begin and End Shapes These shapes are used to begin and end a flowchart The beginning shape has the algorithm name as its label The end shape contains the word End

11 Rectangle Shape Actions Rectangle has one entry and one exit The text in the rectangle is pseudo code corresponding to one step in the algorithm

12 Diamond Shape Decision Point One entry, two exits (one for yes, the other for no ) Contains one question, with yes/no answer

13 Selection Shape Selection is an extension of the decision point Instead of a question, the diamond contains a value The value selects which branch to take One other branch is used for all other values that don t have a branch

14 Connector Shape On page Use for a connection on same page Shape shows connection from one point to another Left shape can be used multiple times Right shape, used once, shows the destination of connection

15 Shapes Combine to Create Structures Straight line structure Single sided branch Double sided branch Selection structure Until loop While loop Do while loop

16 Straight line Structure

17 Single sided Branch

18 Double sided Branch

19 Selection Structure Selection structure is an extension of the branch All branches must converge together at the end

20 First C Program #include <stdio.h> /* printf, scanf definitions */ Int main(void) { } printf( Hello World.\n"); return (0);

21 General Form of a C program preprocessor directives main function heading { } declarations executable statements

22 Function main The point at which program execution begins Contains declarations and executable statements Standard format is: int main(void) { /*declarations*/ */ } /*executable statements*/ return (0);

23 Preprocessor Directives Provide instructions to the preprocessor. Begin with # #include Used to load a library, such as a standard librar #include <stdio.h> /* library needed for scanf, prinf function */ #define Used to define a constant macro Used to define a constant macro #define PI

24 Comments Comments can be written anywhere in the code: any characters between /* and */ are ignored by the compiler and can be used to make the code easier to understand. For example : portion of 1 st line begin with /* to */ are comments #include <stdio.h> /* printf, scanf library definitions */ Int main(void) id) { } printf( Hello World.\n"); return (0);

25 Declarations Statement Variable declarations Thememorycells used for storing a program s input data, output data and its computational results are called variables. The variable declarations tell the C compiler the names of all variables and what kind of information will be stored in each variable. The general format for variable declaration is: Data type variable name or variable list; Example : int count; where int is data type of integer and count is the variable name.

26 Data type Common data type int store integer char store single character Double store real number/floating number

27 String Constants Defined A string constant is zero or more characters (A string constant can be empty) Each character takes one byte in memory (An extra zero byte is used in memory at the end of a string) Each character is encoded using the ASCII code A string constant must begin and end with a double quote (The quote characters are not stored in memory)

28 String Constants Examples "Hello World" "Hello" and "Hello " are different "134.5" is not a number, it's a string "!@#$%;" is a string containing punctuation characters "" is the empty string " " is a string consisting of a space; it's not empty py "AF" and "af" are different case sensitive

29 String Escape Sequences Put special characters in a string or character constant Sequence of characters, starting with backslash \ Put quote or double quote in a string or character constant "\"Hi!\", we said." Single string of 15 characters Put a backslash in a string or character constant "\\" A string with one backslash character Put special codes in a string or character constant "\n" Makes console output start a new line "\t" Outputs a tab character '\g' Make a "beep" noise from the speaker

30 The printf( ) Function Function accepts one or more inputs (called arguments) First argument is a string (called format string) Format string can contain: Text One or more format placeholders, mixed in with text The official name of a format placeholder is a conversion specifier Format placeholders begin with a % character Placeholders ld are only understood dby printf, in its 1 st argument The formatted text prints on the console screen

31 Conversion Specifiers for printf( ) Formatting an int: %d Format as decimal integer 27 %b Format asbinaryinteger integer %x Format as hexadecimal integer 1b %X Format as hex integer using uppercase 1B Formatting a float or double: %f Format as decimal fraction %e Format as scientific notation 1.25e 1 %E Same as %e but with capital E 1.25E 1 Formatting a character: %c Format asaa single character x Formatting a string: %s Format as a string xyzzy g y y For a '%' character must use %%

32 Variables/User Defined Identifiers A variable may be defined using any uppercase or lowercase character, a numerical digit (0 through 9), and the underscore character (_). The first character of the variable may not be a numerical digit or underscore. C reserved word cannot be used as an variable name. Variable names are case sensitive. Valid identifiers letter_1, cent, Hello, Invalid identifier 1Letter double Two*Four big mac Reason invalid Begin with a letter Reserve word Character * not allowed Space is not allowed

33 C Reserved Words auto double include static break elif int struct case else long switch char enum main typedef const extern register union continue float return unsigned default for short void define goto signed volatile do if sizeof while

34 C Program Example with variables #include <stdio.h> /* library definition needed for scanf, prinf function */ #define PI /* Constant needed for circle */ /*This program accepts the radius of a circle, calculates the area, and outputs the radius and the area. */ int main(void) { double radius; /*Stores the radius entered by the user*/ double area; /*Stores the area after the calculation*/ } return (0);

35 Executable Statements An assignment Statements store a value or computational result in a variable, and is used to perform most arithmetic operations in a program. Example : abc = 25; /* assign abc to 25 */ abd = abc + 5 ; kms = KMS_PER_MILE * miles;

36 Input/output functions printf an output function from the I/O (input/output) library (defined in the file stdio.h). scanf an input function from the I/O (input/output) library (defined in thefile stdio.h).

37 scanf Function scanf(format string, input list); For example : scanf("%lf", &miles); Read the floating value into the address of the memory cell referenced dby the variable ibl name miles. Use %d for integer variable and %lf for floating point number variable. The name of each variable that is to be given in value is proceeded by & character.

38 printf Function Prinf(format string, print list); Prinf(format string); function arguments printf("that equals %f kilometers.\n", kms); function name format string print list That equals kilometers

39 C Program Example #include <stdio.h> #define PI /*This program accepts the radius of a circle, calculates the area, and outputs the radius and the area.*/ int main(void) { /*declarations*/ double radius; /*Stores the radius entered dby the user*/ double area; /*Stores the area after the calculation*/ /*executable statements*/ printf("enter the radius of the circle>"); /* output prompt */ scanf("%lf", &radius); /* input radius in floating point format */ area = PI * radius * radius; /*Calculates the area as PI X radius X radius and stores the results in area*/ printf("the area of a circle with a radius of %f is %f\n", radius, area); return (0); }

40 The Software Development Method 1. Specify the problem requirements. 2. Analyze the problem. 3. Design the algorithm to solve the problem. 4. Implement the algorithm. 5. Test and verify the completed program. 6. Maintain and updatetheprogram the program.

41 Algorithm to Program Include required libraries Define constants Declare variables Get the input Perform process to transform input tinto the output Display output t Refine the program

42 Table Arithmetic Operators

43 Unary vs. Binary Operators Unary Operators Binary Operators Take one operand Take two operands Negation ( ) operator Subtraction Plus (+) operator Addition Examples Multiplication x = -y; Division p = +x * y; Examples x = y + z; z = y z;

44 Rules of Precedence Parentheses rule Expressions in parentheses are evaluated separately. Nested parentheses are evaluated from the inside out. Operator precedence rule 1.unary +, 2.*, /, % 3.binary +, Associativity rule Unaryoperators at thesame level are evaluated right to left. Binary operators at the same level are evaluated left to right.

45 Expression Assignment Assignment can cause data to be lost if target variable is of a data type more narrow than the expression double x; int n; x = 9 * 0.5; n = 9 * 0.5; x n

46 Data Type Expression Example m = 3; n = 2; p = 2.0; x = m / p; y = m / n;

47 Casting a Variable's Type

48 Formatting Output of Type int use in prinf output tfunction Table 2.11 Displaying 234 and 234 Using Different Placeholders

49 Formatting Output of Type double use in prinf output function Table 2.13

50 Interactive Mode vs. Batch Mode Interactive Mode Accepts input from users Sends output to the display Batch Mode Accepts input from a file metric <mydata Should echo input using printf Might output data to a file metric >myoutput

51 Input redirection/output redirection Redirect input from file instead of keyboard EXAMPLE : metric metric <mydata Redirect output to a file EXAMPLE : metric >myoutput

52 Program Controlled input and output Files Declare a file pointer variable in which to store the information necessary to permit access to a file. File pointer variable are of type FILE *. Example : FILE *inp, /* pointer to input file */ *opt; /* pointer to output file */ Prepare file to open for read, write inp = fopen("distance distance.dat dat", "r"); r); opt = fopen("distance.out", "w");

53 Interactive program example /* Converts distances from miles to kilometers. */ #include <stdio.h> /* printf, scanf definitions */ #define KMS_PER_MILE /* conversion constant */ Int main(void) { double miles, /* distance in miles */ kms; /* equivalent distance in kilometers */ /* Get and echo the distance in miles. */ printf("enter Distance in miles is "); scanf( "%lf", &miles); printf("the distance in miles is %.2f.\n", miles); /* Convert the distance to kilometers. */ kms = KMS_PER_MILE * miles; /* Display the distance in kilometers. */ printf( "That equals %.2f kilometers.\n", kms); return (0); }

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55 Syntax Errors Code violates a grammar error of C Compiler locates syntax errors during translation Examples: Missing semicolon Undeclared variables Unclosed comments Mismatched open and close braces, quotation marks, or parentheses

56 Runtime Error Detected during program execution Caused by an attempt to perform an illegal operation

57 Logic Errors Errors in the algorithm Causes program to give incorrect results Avoid idby desk checking ki algorithm before bf coding

58 Top Down Design A problem solving method in which you first break a problem into its major subproblems and then solve the subproblems to derive the solution to the original problem. Structure Chart A documentation tool that shows the relationships among the subproblems of a problem.

59 1 59 C Language Elements in Miles to Kilometers Conversion Program

60 Relational and Equality Operators Table 4 1

61 Table 4 2 Sample Conditions

62 Logical Operators And && (temperature > 90) && (humidity > 0.90) Or (salary < MIN_SALARY) (dependents > 5) Not!!(0 <= n && n <= 100)

63 Table 4.6 Operator Precedence

64 Sequential Flow A set of steps that are executed sequentially { statement; statement; statement; } statement statement statement

65 Selection Control Structure Eectionpath Execution changes based on a condition F Condition T Do this Do something else

66

67 Table 4.8 Character Comparisons

68 if Statement with One Alternative if (condition) action to perform if true; if (R!= 0.0) current = voltage / R;

69 if Statement with Two Alternatives if (condition) else action to perform if true; action to perform if false; if (voltage > 3.33 ) printf( A digital High is present!"\n); else printf( A digital Low is present!\n");

70 Blocks if (condition) { statement; statement; } else { statement; statement; } if (condition) { statement; statement; } else { statement; statement; }

71 Nested if Statements if (x > 0) num = num + 1; else { } if (x < 0) num_neg = num_neg + 1; else /* x equals 0 */ num_ zero = num_ zero + 1;

72 Multiple Alternative if Statements /* Display perception of noise loudness */ if (noise_db <= 50) printf( %d decibel noise is quiet.\n, noise_db); else if (noise_db <=70) printf( %d decibal noise is intrusive. \n, noise_db); else if (noise_db <= 90) printf( %d decibel noise is annoying.\n, noise_db); else if (noise_db <= 110) printf( %d decibel noise is very annoying. \n, noise_db); else printf( %d decible noise is uncomfortable. \n, noise_db);

73 Switch Statement The switch statement is used in C to select one of several alternatives. The switch statement is especially useful when the selection is based on the value of a single variable or a simple expression ( called the controlling expression). The value of this expression may be of type int or char, but not of type double. SYNTAX: switch (controlling expression) { label set1 statements1, break; label set2 statements2, break; label setn statementsn, break; default : statementsd, break; } label setn is case constant value :

74 Switch and Flowchart double discount; // Usually code would be read in char code = 'B' ; switch ( code ) { case 'A': discount = 0.0; break; } case 'B': discount = 0.1; break; case 'C': discount = 0.2; break; default: discount = 0.3;

75 Basics of Loops Programming gloops are iterative code structures A set of instructions is repeated a number of times Loops are controlled by a condition, or loop test A loop is preceded by an initialization Sets up the loop condition for initial execution A loop contains an increment Determines whether the loop continues or stops Loops without a loop test repeat indefinitely Useful for control systems or systems that "run continuously"

76 Loop Structures The "while" Loop Loop test is done first, at "top" of loop May or may not execute once or more int count; count = 0; /* Initialization action */ while (count < 5) { /* Loop test (condition) */ /* Loop body - action to repeat */ ++count; /* Loop increment */ }

77 Loop Structures The "do while" Loop Loop test is done last, at "bottom" of loop Always executes at least once int count; count = 0; /* Initialization action */ do { /* Loop body - action to repeat */ ++count; /* Loop increment */ } while (count < 5); /* Loop test (condition) */

78 Loop Structures The "for" Loop The "for" loop Contains initialization, loop test, and increment all in one place int count; for (count = 0; count < 5; ++count) { /* Loop body - action to repeat */ }

79 Different Loops for Different Purposes Counter controlled loop Loops a specific number of times as a counter increments Conditional loop Loops until a specific condition becomes true Sentinel controlled loop Processes data until a special value signals the end Processes data until a special value signals the end of data

80 Modifying Loop Execution The "break" statement break; This is an immediate exit from a loop Only used under unusual circumstances The "continue" statement Used to stop the current loop iteration Begins a new loop execution immediately continue;

81 Structured Code Design principle for code Entry at top of section Exit at bottom of section "Never" use the "goto" statement Very rare circumstances need "break" or "continue" in loop Avoid "spaghetti code" tangled, poorly written code

82 Functions Functions are easy to use; they allow complicated programs to be parcelled up into small blocks, each of which is easier to write, read, and maintain. We have already encountered the function main and made use of I/O and mathematical routines from the standard libraries. Now let's look at some other library functions, and how to write and use our own.

83 Calling a function The call to a function in C simply pyentails referencing its name with the appropriate arguments. The C compiler checks for compatibility between the arguments in the calling sequence and the definition of the function. Library functions are generally not available to us in source form. Argument type checking is accomplished through the use of header files (like stdio.h) which contain all the necessary information. For example, as we saw earlier, in order to use the standard mathematical library you must include math.h via the statement. #include <math.h>

84 1 84 Figure 3.6 Function sqrt as a Black Box

85 1 85 Figure 3.7 Square Root Program

86 1 86 Figure 3.7 Square Root Program (cont d)

87 Writing Your Own Functions 1 A function has the following layout: return type function name ( argument list if necessary ) {...local declarations......statements... return return value; }

88 1 88 Figure 3.23 Function scale

89 1 89 Figure 3.24 Testing Function scale

90 1 90 Figure 3.24 Testing Function scale (cont d)

91 Writing Your Own Functions 22 A function may simply perform a task without returning any value, in which case it has the following layout: void function name ( argument list if necessary ) {...local declarations......statements... }

92 1 92 Figure 3.12 Function draw_ circle

93 Figure 3.15 Flow of Control Between the main Function and a Function Subprogram 1 93