Saurabh Khatri

Lecturer

Department of Computer Technology

VIT, Pune

Unit 2

Selection Statements

Control Statements / Branch Statements

IF-ELSE

Nested IF-ELSE

Conditional Expression

Switch statements

IF…ELSE If (expression) Statement1

Else Statement2

Else is optional

Difference between only if and if-else

Use braces and indents to avoid mistakes

Scope of if and scope of else

Non zero means true

Coding shortcuts (expression) vs (expression != 0) (!expression) vs (expression == 0)

What’s the output?

Int I;

Printf (“Enter value of i “);

Scanf (“%d”, &i);

If (i==5);

Printf(“You entered 5\n”);

Nested IF ELSE

Who does the “else” belong to?

if (n>=0)

for (i=0; i<n; i++)

if (s[i]>0) {

printf(“something”);

return i;

}

else

printf( (“error: n is negative”);

Sample Program

Write a C program to develop Temp. Detector

Between 0 to 10

Very cold!

10 to 20

cool

20 to 30

Pleasant

30 to 40

Hot

ELSE-IF

Multi-way decision

if (expression)

statement

else if (expression)

statement

...

else

statement

Last else is optional

Improves efficiency – by skipping evaluation

SWITCH Multi-way decision

Only to match different constant integer values

All case expressions must be different

All subsequent statements are executed, until

break or return is encountered

Use of Default case

“cases” and “default” can occur in any order

More on SWITCH

Multiple statements do not need to be in braces

What happens when there is a statement without

“case”?

No error, but never gets executed

Switch is more efficient than equivalent if-else –

especially when there are many cases

Sample Program

Write a C program to develop Temp. Detector

using Switch

Between 0 to 10

Very cold!

10 to 20

cool

20 to 30

Pleasant

30 to 40

Hot

Home Assignment 1

Convert your name to decimal equivalent and

then convert to Octal, Binary and Hexa-

Decimal.

Five Problems:

To be solved on a notebook

Submit to CR by 23rd Morning 10.30 am – Sign

on the attendance.

Class test on Saturday Unit 1 collect ppts from

CR.

Iteration Statements A repetition structure allows the programmer to

specify that an action is to be repeated while some

condition remains true.

There are three repetition structures in C,

For

Do-While

While

The while Repetition StructureInit;

while ( condition )

{

statement(s)

Inc/dec

}

If the condition is true, the statement is executed, Then the

condition is evaluated again, and if it is still true, the statement is

executed again till condition becomes false.

The braces are not required if the loop body contains only a single

statement.

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The do-while Statement A do-while statement (also called a do loop) has the

following syntax:

Init;

do{

statement;

}while ( condition );

• The statement is executed once initially, and then the

condition is evaluated

• The statement is executed repeatedly until the condition

becomes false

© 2004 Pearson Addison-Wesley.

All rights reserved5-15

Comparing while and do

statement

true false

condition

evaluated

The while Loop

true

condition

evaluated

statement

false

The do Loop

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The for Statement A for statement has the following syntax:

for ( initialization ; condition ; increment ){

statement;

}

The initialization

is executed once

before the loop begins

The statement is

executed until thecondition becomes false

The increment portion is executed at

the end of each iteration

© 2004 Pearson Addison-Wesley.

All rights reserved5-17

Logic of a for loop

statement

true

condition

evaluated

false

increment

initialization

Code to Evaluate Sum of N natural No.

Void main()

{

int n, i , sum = 0 ;

Scanf(“%d”, &n);

For(i= 0; i<n;i++)

sum = sum +i ;

Printf(“Sum is %d”, sum);

}

Goto Statement

A goto statement in C programming language provides an

unconditional jump from the goto to a labeled statement in

the same function.

Syntax:

label: statement;

……

goto label;

Output

value of a: 10

value of a: 11

value of a: 12

value of a: 13

value of a: 14

value of a: 16

value of a: 17

value of a: 18

value of a: 19

Introduction

There are 2 special statements that can affect the execution

of loop statements (such as a while- for- statement)

The special statements are:

• break

• continue

The break statement

Syntax:

Effect:

break;

• When the break statement is executed inside a loop-

statement, the loop-statement is terminated immediately

The break statement (cont.)

Schematically:

The continue statement

Syntax:

continue;

The continue statement (cont.)

Effect:

•When the continue statement is executed inside a loop-

statement, the program will skip over the remainder of the loop-

body to the end of the loop

The continue statement (cont.)

Effect of a continue statement in a while-loop:

• In the case of a while-loop, when the program reaches end of the loop, the program

will jump back to the testing of the loop-continuation-condition

• the program will skip over the remainder of the loop-body to the end of

the loop

The continue statement (cont.)

Schematically:

Write the Output

Write the Output