Introduction to Computer Programming - CPU1141 Faculty of Natural Sciences Department of Mathematics & Computer Science Bachelor of Science Degree

Transcription

1 Introduction to Computer Programming - CPU1141 Faculty of Natural Sciences Department of Mathematics & Computer Science Bachelor of Science Degree Computer Science: Level 3

2 Course Details Printed Materials: Introduction to Computer Programming Course Material Introduction to Computer Programming Practical Guide Day Schools Practical Sessions Practical Test Continuous Assessment Tests [NBT I & NBT II] Final Exam

3 Course content Computer Programming Introduction to Pascal Data Types & Variables Operations & Expressions Control Structures Functions & Procedures Arrays & Pointers Introduction to C Data Types & Variables Operations & Expressions Control Structures Input output functions Arrays, Strings, Pointers and Functions File Handling

4 Today s Sequence Computer Programming Introduction to Pascal Data Type & Variables Operations & Expressions Control Structures

5

6 Learning Outcome Aim: To provide a brief introduction to the computer programming You will be able to: Get an idea about programming and the level of languages

7 Introduction This chapter discuss the reasons for learning programming and level of languages What is a program? A program is a set of step by step instructions that directs the computer to do the tasks you want it to do and produce the result you want

8 Introduction Why programming? Programming helps you understand computers Writing few simple programs increases your confident level Learning programming lets you find out how you solve problems analytically.

9 Introduction Terms: Programming Language: A set of rules that provides a way of telling a computer what operations to perform

10 Levels of Languages Programming Language mainly divided into two namely Lower and Higher Lower: How close it is to the language of the computer eg: 1 s and 0 s Higher: How close it is to the language of people use eg: similar to English language

11 Levels of Languages There are five levels of language: Machine Language Assembly Language High-Level Language Very High-Level Language Natural Language

12 Levels of Languages Machine Language: The lowest level of programming language Only understood by the computer and IMPOSSIBLE for humans Each type of computer has its own machine language Represent the data and program instructions as 1s and 0s These 1s and 0s are corresponded to the ON and OFF electrical states in the computer respectively.

13 Levels of Languages Assembly Language: Used abbreviation which are easily remembered by human to replace 1s and 0s Eg: ADD, MUL Each type of computer has its own assembly language Requires a translator called Assembler to convert the assembly language program into machine language Assembly Language Translator ( Assembler) Machine Language

14 Levels of Languages High-Level Language: Began using of High-Level language in early 1960 Programs were written in similar to English Language Eg: COBOL, Fortran, Pascal, C, C++, C# Runs on any machine Benefits: Convenient More production with less effort Tend to focus on solving much complex problems

15 Levels of Languages High-Level Language: A translator called Compiler is needed to translate the symbolic statements into machine language Source Code Translator ( Compiler) Object Code Programmers write programs in a form called Source Code Compiler is used to translate source code to machine language The compiler produces an intermediary form called object code Object code is much similar to a computer s machine language

16 Levels of Languages Very High-Level Language: These are known by their generation number; fourth generation languages (4GLs) 4GL languages are programming languages closer to human languages than typical high level languages Mostly used to access databases

17 Levels of Languages Natural Language: These are used for artificial intelligence and neural networks Eg: Prolog Prolog is used to develop Expert Systems

18 PART A: PASCAL LANGUAGE

19 Learning Outcomes Aims: To provide a brief introduction to the Pascal Language You will be able to: Identify the major segments of a Pascal program Write a simple Pascal program

20 Introduction Major segments of a Pascal Program: A Pascal program has three major segments: The program identification and description segment The declaration segment The main body of the program

21 Introduction Segment 1: Program Identification & Description: The structure of the first line in the program PROGRAM example01 (INPUT, OUTPUT); Explanation: Code PROGRAM example01 (INPUT, OUTPUT) Description First word of any Pascal program Program Name To indicate whether program has any input or output ; Last character of any Pascal line

22 Introduction Segment 1: Program Identification & Description: Every Pascal line should end with a semicolon ; So, it is possible to spread one Pascal line over a no. of horizontal lines Pascal is not case sensitive language Upper case characters were used to represent keywords in examples

23 Introduction Segment 1: Program Identification & Description: Rules in Pascal for giving program name to a program: Name has to start with a letter of the alphabet a-z or an underscore _ Do not start a program name with a digit or special characters #,? The other items in a name could contain any keyboard character There should be no blank space within a name Eg: if a name contain 2 components, it can be separated using an underscore Do not include keywords used in Pascal for naming a program

24 Introduction Segment 1: Program Identification & Description: Keywords in Pascal: And Downto If Or Then Array Else In Packed To Begin End Label Procedu re Progra m Type Case File Mod Until Const For Nil Record Var Div Functi on Not Repeat While Do Goto Of Set wit h

25 Introduction Segment 2: Declaration: Define variables, constants etc. in the program All of the entities going to be used in the program must be defined For that, data types and variables will be deeply discussed in chapter 2

26 Introduction Segment 3: Main body of the program: Main body of the program is written within BEGIN-END pair This is equivalent to a set of brackets It is possible to have any no. of BEGIN-END pairs in a single program However, no. of BEGIN statements should match no. of END statements

27 Introduction Segment 3: Main body of the program: Example: PROGRAM firstprogram (OUTPUT); BEGIN WRITELN ( Hello my friend ); END

28 Introduction Displaying output : WRITELN, WRITE command To display several lines of text you need a WRITELN statement for each line Example PROGRAM lineoftext (OUTPUT); BEGIN WRITELN ( Hi there ); WRITELN ( How are you today? ); WRITELN ( Are you ready for Pascal ) END

29 Introduction Displaying output : WRITELN, WRITE command Explanation: Each statement must be separated from the next one with semicolon This is the only way the compiler can recognize the end of the statement But, you may skip the semicolon in the last statement of the program block

30 Introduction Displaying output : WRITELN, WRITE command Output: Hi there How are you today? Are you ready for Pascal The WRITELN statement displays a line of text followed by a new line Use WRITE statement, if you want to display two string on the same line

31 Introduction Displaying output : WRITELN, WRITE command Code: PROGRAM Twolines (OUTPUT); BEGIN WRITE ( Hi there ); WRITELN ( How are you today? ); WRITELN ( Are you ready for Pascal ) END Output: Hi there How are you today? Are you ready for Pascal

32 Introduction Displaying output : WRITELN, WRITE command To display the content of the variable you need a WRITELN or WRITE statement without using quotes Also WRITELN or WRITE can be used to display text and content of variables in the same statement by separating them with a coma WRITELN ( The Result is =, r);

33 Introduction Comments: Comments are enclosed with braces or bracket and a star in cases (*This is a comment*) Can be included in anywhere in the program Compiler ignores the comment Comments are useful to explain the program to a human reader

34 Introduction Indentations: It is customary to a line each BEGIN-END pair along the same vertical line Eg: five horizontal spaces should be kept from the previous block when starting a new

35 PART A: PASCAL LANGUAGE

36 Learning Outcomes Aims: To provide an overview of some significant features of the Pascal Language You will be able to: Identify the data types in Pascal Language Get an idea about declaring the variable and constant Learn how to format you numeric outputs

37 Data Types When writing program, it is necessary to store information in component form to manipulate them later For that, variables are used Every variable should have a name and a type Type mean the values that the variable can take It helps to determine the amount of memory space to store a variable

38 Data Types Variable should be declared in the declaration section There are no. of standard data types Integer Real Boolean Char

39 Data Types Integer: This type allows to represent, store and process integer numbers Contains all the integer values in the range of; -maxint,., -1, 0,+1,.,+maxint The value of maxint is on minicomputer in large computers So, outcome of any arithmetic on integer values will be correct only of they are in ± maxint Or else, the answers will be unpredictable (overflow)

40 Data Types Real: Real numbers are numbers with decimal values eg: meters, 9.2 seconds The limit of the real numbers which can be stored in a computer is very large compared to integers

41 Data Types BOOLEAN: Can only have two values True False Normal arithmetic operations cannot be performed on a boolean variable

42 Data Types Char: Can hold any single given character at a time Eg: if x is char variable, it can hold only one character at a time Blank space also considered as a character When assigning char variable, enclosed the character with single quotes Eg: A Each char requires a one byte of memory

43 Variables Variable is a location in memory referenced by a variable name (identifier) where a data can be stored Can hold only one value at a time during the program execution Values can be changed during several executions

44 Variables Variable Names: A variable must be declared before using the program Variables are the identifiers When declaring a variable, it consists with Sequence of letters and digits First character should be either a letter or underscore Keywords cannot be used

45 Variables Variable Declaration: The type and the name of a variable should be initiate before using a program It should be declared in the declaration part in the program Declaration part starts with the keyword VAR Eg: VAR gross_salary : REAL; n, i : INTEGER name : CHAR;

46 Variables Variable Declaration: Eg1: Following equation gives the total resistance R of three resisters r1, r2 and r3 connected in parallel The programmer should consider before writing the program for the above problem, Read the values for r1, r2 and r3 Calculate R Print the result

47 Variables Variable Declaration: Eg1: Line 1 Line 2 Line 3 Line 4 Line 5 Line 6 Line 7 Line 8 Line 9 Line 10 PROGRAM calc_of_resistance (INPUT, OUTPUT); VAR r1,r2,r3,r : REAL; BEGIN WRITE ( Enter three resisters: ); READLN ( r1,r2,r3 ); R :=1/r1+1/r2+1/r3; R := 1/R; WRITELN ( Total Resistance is, R); END.

48 Variables Variable Declaration : Explanation: Line 1: Program naming Line 2: variable naming and declaration Line 4-10 : solving the given problem Line 6: Reading the user inputs for r1, r2, and r3 Line 7: calculating the R with given r1, r2 and r3 Line 8: replacing the R with value of 1/R Line 9: printing the calculated value for R

49 Variables Variable Declaration : how practically run a program for Eg1 Enter the given program Save and compile it Compiler show if any syntax errors available Fix them until the program is free from syntax errors When the compilation is successful you are ready to run the program The computer waits until you put three values for r1, r2 and r3 when the program runs Once entered values, the total resistance will be displayed Enter three resisters: Total Resistance is : E-01

50 Variables Reading from the keyboard: READLN, READ: READLN and READ commands in Pascal program are used to read values given by user to produce results READ: is used to read a value of one variable at a time Eg: READ (variable) / READ (r1); READLN: is used to read the value of one or more variables Eg: READLN (variable_list) / READLN (r1,r2,r3);

51 Variables Formatting Output: You can format your output in a fixed notation Eg1: WRITELN ( Total Resistance is, R:8:2); The format 8:2 determines a field width of 8 positions including 2 decimal places Total Resistance is : *******0.92

52 Variables Constants : A constant remains unchanged throughout the execution of the program It is often useful to give a symbolic name (identifier) to a constant This can then be used throughout the program whenever the value of the constant is required Eg: if the program replace with pi, it would be much easier to read

53 Variables Constants : Keyword CONST is used to declare constants in the declaration segment of the program Syntax: Example: CONST identifier = constant; CONST pi = 22/7;

54 PART A: PASCAL LANGUAGE

55 Learning Outcomes Aims: To provide an overview of some important features of the Pascal Language You will be able to: Learn various operators and their precedence in Pascal

56 Types of Operators The operators define how the variables and constants in and expression will be manipulated Three operators allowed in Pascal; Arithmetic Operators Relational Operators Logical Operators

57 Types of Operators Expression: An Expression is a combination of variables, constants and operators written according to the syntax of the language Eg: a + b a + 200*w total + x/3

58 Types of Operators Arithmetic Operators: Basic arithmetic operations + : addition - : subtraction * : multiplication / : division These operators act as usual operators The entities on which the operators are applied are called as Operands Eg: o 5+3 o Here, 5 and 3 are operands and + is the operator

59 Types of Operators Arithmetic Operators: Additionally, DIV and MOD are used as operators Eg: For integer division, DIV is used [a DIV b] Divide a by b and give the divisor 10 DIV 5 = 2 MOD is used to get the remainder of integer division [a MOD b] Divide a by b and give the remainder 10 MOD 5 = 0

60 Types of Operators Relational Operators: A relational operator is used to make comparisons between two expressions Allowed relational operators in Pascal; Operator Usage = Equal to < Less than > Grater than <> Not equal to <= Less than or equal to >= Grater than or equal to

61 Types of Operators Relational Operators: Each one of the operator compares its left hand side operand with its right hand side operand Operands can be variables or expressions The whole expression involving the relational operator then evaluates to an integer

62 Types of Operators Logical Operators: Logical operators let you combine two or more relational expressions into a single expression which evaluates to either true or false Eg for Pascal logical operators; NOT AND OR

63 Types of Operators Logical Operators: AND Operator Expression 1 Expression 2 Result True True True True False False False True False False False False

64 Types of Operators Logical Operators: OR Operator Expression 1 Expression 2 Result True True True True False True False True True False False False Logical Operators: NOT Operator Expression True False Result False True

65 Operator Precedence Operators are used in a program according to their priority order (precedence) as follows; Operation Symbol Precedence Multiplication *, /, DIV, MOD 1 Addition +, - 2 Relation =, <, >, <>, <=, >= Logical NOT 4 3 AND 5 OR 6

66 Operator Precedence Brackets always have higher precedence than all the above operators If bracket used; The content inside the innermost pair of brackets will be evaluated first When several operations having same precedence; Evaluation will be done in left to right

67 Character operations In addition to the comparison statements, following are used as operators ORD SUCC PRED CHR

68 Character operations ORD: ORD function has one argument which should be a character or a character variable It will return an integer number corresponding to the internal representation If ASCII is used, then the ORD function will return the corresponding ASCII value

69 Character operations CHR: CHR function takes an integer as an input argument and returns the corresponding character Opposite of the ORD function SUCC: SUCC function takes a single character or a character variable as an argument Returns the next character

70 Character operations PRED: PRED function takes a single character or a character variable as the input argument Returns the previous character

71 PART A: PASCAL LANGUAGE

72 Learning Outcomes Aims: To provide an overview of control structures in Pascal Language You will be able to: Use the major control structures such as repetition loops conditional statements in Pascal Language

73 Control Structures For practical use of computers, selective and repetitive expressions are necessary Conditional statements: There are two main types of statements in Pascal for selective operations IF-THEN CASE

74 Conditional Statements IF-THEN: Use when we have to select a set of actions from two sets depending on a condition IF condition THEN statement ELSE statement; However, the ELSE is optional IF-THEN and IF-THEN-ELSE statements are treated as one compound statement So, a semicolon is used only at the end

75 Conditional Statements IF-THEN: The condition with IF must produce a boolean result The boolean expression is evaluated If it is true, The statements following THEN will be executed Otherwise, The statements following ELSE will be executed If there are more than one statement with IF-THEN or ELSE statements, they are grouped with BEGIN- END

76 Conditional Statements IF-THEN: Example: IF A > B THEN max := A ELSE max := B; ELSE-IF statements are used to make multi-way decision based on several conditions This is done by cascading several comparisons As soon as one of a else-if gives a true result, corresponding statements will be executed and no further comparisons will be performed

77 Conditional Statements ELSE-IF: Example: IF (result >= 75) THEN WRITELN ( Passed: Grade A ) ELSE IF (result >= 60) THEN WRITELN ( Passed: Grade B ) ELSE IF (result >= 45) THEN WRITELN ( Passed: Grade C ) ELSE WRITELN ( Failed );

78 Conditional Statements Nested IF Statements: IF statement inside the other IF statements are known as Nested IF Statement If there is a problem that involved with more than two alternatives courses of action can be coded using nested if statement In the nested if, the else statement is always associated with the nearest if statement

79 Conditional Statements Nested IF Statements: Example: IF i > 10 THEN BEGIN WRITELN ( i is more than 10 ); IF j > 3 THEN WRITELN ( j is more than 3 ); ELSE WRITELN ( j is less than or equal to 3 ); END ELSE WRITELN ( i is less than equal to 10 );

80 Conditional Statements IF Statements: Example: Write a program in Pascal to read a set of numbers and to find the maximum value. The program should be terminated when a-1 is read Refer page 22

81 Conditional Statements CASE Statements: CASE statement allows the choice of one out of several sets of action The selection is done by matching the value of the selector with a case label attached to each statement

82 Conditional Statements CASE Statements: CASE selector OF case label1: statement case label2: statement.. case labeln: statement ELSE statement END;

83 Conditional Statements CASE Statements: Depending on the selection value, the case statement will pick the appropriate action If the SELECTOR has a value for which no action has been described, then the ELSE statement is executed CASE month OF 1,3,5,7,8,10,12: no. of days := 31; 2 : no. of days := 28; 4,6,9,11 : no. of days := 30; END;

84 Conditional Statements CASE Statements: If there is value range then the CASE statement are written as follow; CASE mark OF : grade := F ; : grade := C ; : grade := B ; : grade := A ; END;

85 Conditional Statements CASE Statements: Example: Write a program to read a number between 1-7. if the number is 1 then print Monday. If it is 2 then print Tuesday and so on.

86 CASE Statements: Example: PROGRAM eg_case(input, OUTPUT); VAR number : INTEGER; BEGIN WRITELN( Enter a number within 1-7: ); READLN(number); END. CASE number OF 1 : WRITELN( Monday ); 2 : WRITELN( Tuesday ); 3 : WRITELN( Wednesday ); 4 : WRITELN( Thursday ); 5 : WRITELN( Friday ); 6 : WRITELN( Saturday ); 7 : WRITELN( Sunday ); ELSE WRITELN( Invalid day of the week!!! ); END;

87 Repetition There are three main types of statements for repeating certain instructions REPEAT UNTIL Loop WHILE Loop FOR Loop

88 Repetition REPEAT-UNTIL Loop: This will repeat everything that is inside this loop, as the condition given with the until statement is false When the statement becomes true, the loop is completed Any statements after UNTIL are then executed The expression supplied with the UNTIL statement must give a boolean value

89 Repetition REPEAT-UNTIL Loop: Example: REPEAT statement(s) UNTIL boolean_expression; x:=1; REPEAT WRITELN(x); x:= x +1; UNTIL x > 10;

90 Repetition REPEAT-UNTIL Loop: Example: Write a program to read a set of integer numbers and to calculate the total and the average. The end of the list of numbers is denoted by -1.

91 REPEAT-UNTIL Loop: Example PROGRAM eg_repeatuntil(input, OUTPUT); CONST endmark = -1; VAR value, total, count, avg : INTEGER; BEGIN total := 0; count := 0; avg := 0; REPEAT WRITELN( Enter a number: ); READLN(value); count := count + 1; total := total + value; avg := total DIV count; END. WRITELN( The total is:, total, and the average is:, avg); UNTIL value = endmark;

92 Repetition REPEAT-UNTIL Loop: Example: This program will add the endmark (-1) to the output. So this should be corrected as follows

93 REPEAT-UNTIL Loop: Example PROGRAM eg_repeatuntil(input, OUTPUT); CONST endmark = -1; VAR value, total, count, avg : INTEGER; BEGIN total := 0; count := 0; avg := 0; WRITELN( Enter a number: ); READLN(value); REPEAT count := count + 1; total := total + value; avg := total DIV count; WRITELN( The total is:, total, and the average is:, avg); WRITELN( Enter a number: ); READLN(value); END. UNTIL value = endmark;

94 Repetition REPEAT-UNTIL Loop: Example: This program will do the answers correctly as follows;

95 Repetition WHILE Loop: WHILE loop checks the condition at the beginning So the constants within the loop may or may not be executed WHILE loop will be executed as long as the condition is true If there are more than one statement with the WHILE statement, they can be grouped with BEGIN-END

96 Repetition WHILE Loop: Example: WHILE boolean_expression DO statement; x:=1; WHILE x <=10 DO BEGIN WRITELN(x); x:= x +1; END;

97 REPEAT-UNTIL Loop: Example using WHILE PROGRAM eg_while(input, OUTPUT); CONST endmark = -1; VAR value, total, count, avg : INTEGER; BEGIN total := 0; count := 0; avg := 0; WRITELN( Enter a number: ); READLN(value); WHILE value <> endmark DO BEGIN count := count + 1; total := total + value; avg := total DIV count; END. END; WRITELN( The total is:, total, and the average is:, avg); WRITELN( Enter a number: ); READLN(value);

98 Repetition FOR Loop: Used in repeating a loop for several times FOR a := b TO c DO a, b and c could be any data type for which it is possible to go from b to c in a finite no. of increments a,b and c are real variables Most cases they will be integers

99 Repetition FOR Loop: FOR a:=b DOWNTO c DO In this loop, the values are decreased from b to c If there are more than one statement with the FOR statement, they are grouped with BEGIN- END

100 Repetition FOR Loop: FOR control_variable:= initial TO/ DOWNTO DO statement; Example: FOR x:= 1 TO 10 DO WRITELN (x); FOR x:= 10 DOWNTO 1 DO WRITELN (x);

101 REPEAT-UNTIL Loop: Example using FOR LOOP to find the total and average of 5 numbers PROGRAM eg_for(input, OUTPUT); VAR value, total, count, avg : INTEGER; i : INTEGER; BEGIN total := 0; count := 0; avg := 0; FOR i := 1 TO 5 DO BEGIN WRITELN( Enter a number: ); READLN(value); count := count + 1; total := total + value; avg := total DIV count; END. END; WRITELN( The total is:, total, and the average is:, avg);