Week 4 Program Control Structure Sequence and Selection control structure Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Outline Types of program control structure Sequence control Selection Types of selection One-way selection Two-way selection Multi-selection Compound statement Nested if Conditional operator Switch structure Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Discussion on Lab Exercise 3 : Introduction to LINUX Lab Exercise 4 : Getting Started with C Programming Sem1-06/07 EKT120: Computer Programming

Types of Program Control Structure Sequence Branch or Decision Loop Sem1-06/07 EKT120: Computer Programming

Sequence Control Structure The most common and basic structure of a program A set of instructions in sequence from top to bottom Statements executed one after the other in the order in which they are written-sequential execution Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Example Write a program that creates a table of degrees Celsius with degrees Fahrenheit. Begins at 0 degree and proceed to 100 degree in 20 degree increments. Use no more than 2 variable in your program. Solution The equation F = C + 32 C = degree Celsius F = degree Fahrenheit 9 5 Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Specify Example Perform the pre calculation to expect the correct output for example…. C F 32 20 68 40 104 60 140 80 176 100 212 Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Algorithm (pseudo code) Begin, Declare variables Print headings of table set C = 0 calculate F print C and F set C = 20 . End Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Start Float C,F Algorithm (Flow chart) C=0 F=(9/5)*C + 32 Print C,F C=20 F=(9/5)*C + 32 Print C,F End Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Pseudocode Flowchart C Program Begin Declare variable Print heading Set C = 0 Calculate F Print C and F Set C = 20 Set C = 40 Set C = 60 Set C = 80 Set C = 100 End #include <stdio.h> Void main (void) { float C, F; printf(“Table of Celcius and Fahrenheit”); printf(“Celcius\t\tFahrenheit”); C =20.; F =(9./5.)*C + 32.; printf(“%8.2f\t\t%8.2f”,C, F); C =40.; F :=(9./5.)*C + 32.; C =60.; F :=(9./5.)*C + 32.; C :=80.; F :=(9./5.)*C + 32.; C :=100.; F :=(9./5.)*C + 32.; } Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Explanation 9 5 The equation F = C + 32 The program equation F =(9/5)*C + 32; Command printf(“%8.2f\t\t%8.2f”,C, F); Print format to print float number with 8 numbers or field width and at 2 decimal points. Semicolon ; must have at the end of C command. Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Selection structure Used to choose among alternative courses of action C has three types: if, if..else switch Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Selection Statements Used to control the flow of a program Also called as decision or branches Branches are conditions or choices used to enable selection of program flow Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Types of selection One-way selection = if Two-way selection = if..else Multi-selection Nested if Switch structure = switch Sem1-06/07 EKT120: Computer Programming

Review: Relational Operator Equal To (equality) == Less Than < Greater Than > Less than or equal to <= Greater than or equal to >= Not Equal to !> Sem1-06/07 EKT120: Computer Programming

The if selection structure if structure is a single-entry/single-exit structure Pseudo code Flowchart begin if student’s grade is greater than or equal to 60 Print “Passed” end False Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming One-way selection in C Example 1: if (grade >= 60) printf(“Passed\n”); ….. Comment.. (grade>=60) – This is a relation statement which result in logic TRUE or FALSE. If the statement (grade >=60) is true the the command printf(Passed\n) shall be executed. Sem1-06/07 EKT120: Computer Programming

One-way Selection- example char grade; …… if(markah>= 90) grade = 'A'; …... printf(“Grade is : %c\n”, grade); Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming One-way Selection = if In C, a condition is represented by a logical (Boolean) expression True and False are logical (Boolean) values The syntax of one-way selection is: if (expression) statement; If the value of the expression is true, statement is executed; if false, statement is not executed and the computer goes on to the next statement in the program. Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming One-way Selection = if Example 3: if (temperature is greater than 27 degree and it is not raining) recommended activity is golfing bool rain=false; … If ((temp > 27) && !(rain)) printf(“recommended activity is golfing”); And not Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming One-way Selection = if Common Errors if score >= 90 //no parentheses grade = 'A'; if(score >= 90); //; not here Sem1-06/07 EKT120: Computer Programming

Two-way Selection = if..else The syntax of two-way selection is: if (expression) statement1; else statement2; If the value of the expression is true, statement1 is executed; if false, statement2 is executed Relational exp, or logical exp Sem1-06/07 EKT120: Computer Programming

The if..else selection structure Specifies an action to be performed both when the condition is true and when it is false Pseudocode Flowchart begin if student’s grade greater than or equal to 60 then Print “Passed” else Print “Failed” end Display FAILED PASSED Sem1-06/07 EKT120: Computer Programming

Two-way Selection - if..else in C ……… if (grade >=60) printf(“Passed\n”); else printf(“Failed\n”); …… Execute if true Execute if false Sem1-06/07 EKT120: Computer Programming

Two-way Selection = if..else Another example: if (hours > 40.0) //Line 1 wages = 40.0*rate+1.5*rate*hours - 40.0); //Line 2 else //Line 3 wages = hours * rate; //Line 4 If hours is 50, then the statement at Line 2 executes If hours is 30, then the statement at Line 4 executes Sem1-06/07 EKT120: Computer Programming

Multi-selection = if-else if The syntax is: if(exp1) statement1; else if(exp2) statement2; else if(exp3) statement3; … else statement n; An if-else if control structure shifts program control, step by step, through a series of statement blocks. Sem1-06/07 EKT120: Computer Programming

Multi-selection if-else if Example 1: Write a C program that can display the results and the corresponding grades as illustrated in the table Hint : Use flowchart or pseudocode. marks grade 90 – 100 A 80 – 89 B 70 – 79 C 60 – 69 D 0 – 59 F Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Flowchart Sem1-06/07 EKT120: Computer Programming

Multi-selection - if-else if in C if(mark >= 90) printf( “Grade = A\n”); else if(mark >=80) printf(“Grade = B\n”); else if(mark >=70) printf(“Grade = C\n”); else if (mark >= 60) printf( “Grade = D\n”); else printf(“Grade = F); Sem1-06/07 EKT120: Computer Programming

Compound (Block of) Statement Several statements in a body. A set of statements contained within a pair braces. A compound statement (also called a block of statements) takes the form { statement 1; statement 2; . statement n; } It is considered a single statement Sem1-06/07 EKT120: Computer Programming

Compound (Block of) Statement Example: if(mark >= 90) { printf(“Pass\n”); printf(“Grade = A\n”);} else if(mark >=80){ printf(“Pass”\n”); printf(“Grade = B\n”);} else if(mark >=70){ printf(“Grade = C\n”);} else if (mark >= 60){ printf( “Grade = D\n”);} else {printf(“Pass”\n”); printf(“Grade = F);} A Block if statement. If the relational expression is true, the statement in “true” block is (between 2 braces) are executed. Otherwise, the entire block of statements is ignored) False ? Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Nested if When one control statement is within another, it is said to be nested if(exp1) if(exp2) { statement1; statement2; } { statement1; statement2; } Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Nested if Example if (temperature >= 50) { if (temperature >= 80) printf( "Good day for swimming.\n”); else printf( "Good day for golfing.\n“); } printf("Good day to play tennis.\n“); Sem1-06/07 EKT120: Computer Programming

The Conditional Operator The syntax of using the conditional operator is: expression1 ? expression2 : expression3; This is called a conditional expression. The statement: if (a >= b) max = a; else max = b; Is equivalent to the statement: max = (a >= b) ? a : b; Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Switch Structures Similar to if-else if control structure The general form (syntax): switch (expression) { case value1: statements1; break; case value2: statements2; break; . case valuen: statementsn; break; default: statements; } Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Switch Structures The break statement has a special meaning and may or may not appear after each statement. In C, switch, case, break, and default are reserved words. In a switch structure, first the expression is evaluated. The value of the expression is then used to perform the corresponding action. Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Switch Structures The expression is usually an identifier. The value of the expression can be only integral. The expression is sometimes called the selector. Its value determines which statement is selected for execution. A particular case value should appear only once. One or more statements may follow a case label, so you do not need to use braces to turn multiple statements into a single compound statement. The break statement may or may not appear after each statement. Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Switch Structures Example: switch (grade) { case 'A': printf("The grade is A.“); break; case 'B': printf("The grade is B.“); break; case 'C': printf("The grade is C.“); break; case 'D': printf("The grade is D.“); break; case 'F': printf("The grade is F.“); break; default: printf("The grade is invalid.“); } where, grade is a variable of the type char. If the value of grade is, say 'A', the output is The grade is A. Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Switch Structures The switch statement executes according to the following rules: When the value of the expression is matched against a case value (also called a label), the statements execute until either a break statement is found or the end of the switch structure is reached. If the value of the expression does not match any of the case values, the statements following the default label execute. If the switch structure has no default label, and if the value of the expression does not match any of the case values, the entire switch statement is skipped. A break statement causes an immediate exit from the switch structure Sem1-06/07 EKT120: Computer Programming

EKT120: Computer Programming Summary Sem1-06/07 EKT120: Computer Programming