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Loops

Pretest loops

post test loops

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Pretest loop- first test condition should be

evaluated if it true executes the body of the

loop.-while and for loopspost test loop- first body of the loop is executed

after that condition would be tested.

do-while.

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Looping process include 4 steps

1.Loop counter initialization

2. test the condition.

3. execute the body of the loop.4.increment or decrement the loop counter.

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While Statements

The "while" loop is a generalized looping structure that employs avariable or expression for testing the ending condition.

Is a repetition statement that allows an action to be repeated while some

conditions remains true. Variables used in the loop control testing must be initialized

Testing for the termination condition is done at the top of the while() loop

The body of WHILE statement can be a single statement or compound

statements

Syntax:

Form 1: Simple Statement

while (condition)

statement;Form 2: Compound Statements

while (condition)

{ s1; s2; s3; ..}

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While statement

The statement (or a block of statements) is executedThe statement (or a block of statements) is executed

repetitively until the condition becomes false.repetitively until the condition becomes false.

while ( condition )

statement;

whilewhile is ais a

reserved wordreserved word If the condition is true, theIf the condition is true, the

statement is executed.statement is executed.

Then the condition isThen the condition is

evaluated again.evaluated again.

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Tips on while loop

1. Statements within the while loop would keep on executed until the conditionbecomes false. Then the control passes to the first statement after the while loop.

2. Condition may be any valid expression

while(i=10&&j

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4. Condition must eventually become false.otherwise the loop would be executedforever indefinitely.

main()

{

int i=1;

while(i

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5. Loop counter can also decremented to execute the body of theloop repeatedly.

main()

{

int x=10;

while(x>=1)

{

printf(%d\n,x);

x=x-1;

}//while

}//main

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6. Loop counter can also be float need not be in int.

main()

{

float x=2.0;while(x

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What is the output of the following program.

main()

{

int x=1;while(x

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No, it doesnt print numbers from 1 to 32767

goes to indefinite loop.

main()

{

int x=1;

while(x

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Program to compute y=xpow n

main()

{

int i=1,n,x,y=1;

printf(enter the value of x:);

scanf(%d,&x);

printf(enter the n value);

scanf(%d,&n);

while(i

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Nesting of while loops

While loops within the other while loop.

Write a program to generate the given format

using while loops1

2 3

4 5 67 8 9 10

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main()

{

int n,i=1,j=1,k=1;

printf(\n enter the n value);

scanf(%d, &n);

while(i

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The do while statement

Statements in the loop are executedfirst (at least once, and condition istested last

Loop is controlled by a condition orcounter

Syntax

do {

statement;

statement;

} while (condition);

statement;

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While example

#include

int main(){

int i = 1, sum = 0;

while ( i 1);

printf(Factorial of 5=%d,result);

}

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Program to reverse a number

main()

{

int n,x,y=0;

printf(enter the number);

scanf(%d, &n);

do{

x=n%10;

y=(y*10)+x;

n=n/10;

}while (n>0);printf(\n the reverse number is %d,y);

getch();

}//main

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The for Loop

When the number of passesthrough a loop is known inadvance, a for statement is often

used

for(expr1; expr2; expr3)

statement;

expr1 controls the looping action,expr2 represents a condition that

ensures loop continuation, expr3modifies the value of the controlvariable initially assigned by expr1

When a for statement is executed, expr2 is evaluated and testedat the beginning of each pass through the loop. expr3 is

evaluated at the end of each passIf the loop continuation condition is initially false, the body partof the loop is not performed

Any of the three parts can be omitted, but the semicolons mustbe kept

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for (i=1; i

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Few points on for loop

1. Counter variable is initialized only once when thefor statement is executed for the first time.

2. The condition is tested. If it is true the body of theloop is executed.

3. When it reaches to the closed braces, the control issend back to the for statement, where the value ofthe variable gets incremented or decremented

4. Again the test is performed, if true it enters into the

next iteration.5. The body of the loop executed repeatedly until the

condition becomes false.

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Few points on for loop

6. initialization, testing and increment part of a loop can be replaced by anyvalid expression.

ex:

for(x=10;x;x--)

for(i

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Few tips on for loop7. We can omit any part of the for statement but we need to keep semicolons

int I;

for(i=1;i

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Nested forloops

Nested means there is a loop within a loop

Executed from the inside out

Each loop is like a layer and has its own counter variable, its own loopexpression and its own loop body

In a nested loop, for each value of the outermost counter variable, thecomplete inner loop will be executed until it satisfies its condition.

General formfor(loop1_exprs) {

loop_body_1a

for(loop2_exprs) {

loop_body_2

}

loop_body_1b

}

Most compilersallow 15 nestinglevels DONTDO IT!!

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#include

#include

int main()

{

int n,i=1,j=1;

clrscr();

printf(enter n value\n);

scanf(%d,&n);

for(i=1;i

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Output

enter the n value

12 2

3 3 3

4 4 4 4

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Multiple initialization of for loop

* The initialization part of the for loop can have more than onevariable initialization separated by a comma.

ex:

for(i=0,j=0;j

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Program to find whether the

number is prime or not#include#include

int main()

{

int n,i,counter=1;

clrscr();

printf(enter the number\n);

scanf(%d,&n);for(i=1;i

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Break statement

-When you want to jump out of the loop

instantly use keyword break

-W

hen a break is used inside the loop, controlautomatically passes to the statement which

immediately follows the loop.e

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Write a program to whether a given

number is prime or notmain()

{

int n,i=2;

printf(enter the number\n);

scanf(%d, &n);

while(i

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GOTO statement

Used to alter the sequence of program execution by transferring control(jump) to some other parts of the program.

The goto statement in C allowsthe transfer of control from one

position to another position in the

same program.

The destination must be marked

with a label.

The general syntax:

label: statement;

The syntax for goto:

goto label;

Main()

{

. . .

If (. . . ) goto End;

. . .

End:

. . .

}

The goto statement

allows one to jumpfrom any place to

anywhere else within afunction.

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- Using goto we can move from forward to backward and vice-versa

example

int i=0,total=0;

sum:total=toatal+i;

i++;

if(i

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Continue statement

- To take the control to the beginning of the loop, by skippingsome statements inside the loop.

- use keyword continue

ex:-

int i=1,j=0;While(i

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BREAK and CONTINUE

- break; causes an exit from the innermost loop or switch.terminate : for, while, do while, and switch

- continue; causes the current iteration of a loop to stop

and the next iteration to begin immediately.effective only in : for,while and do while

Break Example

.....while (1){

scanf("%f", &x);

if (x < 0.0)

break;

/* exit loop if the value is

negative */printf("\n%f", sqrt(x));

....

}

/* break jumps to here */

Continue Example

. . . . . .

for (i = 0; i < TOTAL; ++i){

c = getchar();

if ( '0'