## Loop

LOOP's :-

In programming sometime we require to execute a set of instruction more from one time . For this purpose " C " provide loops . In loop , we can execute set of instruction with  or  without any changes .  It also prevent the repetition of the same instruction & make compact code .

C provide three type of Loops :- while Loop :-

while loop is generally use in problem where it is not known in advance that how many time the loop execute.while loop is a Pre-test loop ie. Firstly the condition is check , if it give Non-zero result so-only the statement block is executed . Otherwise it leave the statement block .

Syntax :-
while(condition)
{

statement block

}

Working :-  The while loop follow the following steps .

First it check the condition .
If the condition give Non-Zero result so the statement-block execute & repeat the first step .
If the condition give Zero as result so it leave the statement-block inside the loop & execute rest of the instructions .

Þ In while loop we can use any type of valid expression & the statement-block execute only if the expresssion return a Non-Zero result .
while(expression)
{
statement block
}

 EXPRESSION Non-Zero = TRUE Zero = FALSE 1) while( 1 ) { } 1) while( 0 ) { } 2) int i=5 ; while(i) { } 2) int i=0 ; while(i) { } 3) int i ; while(i = 8) { } 3) int i ; while(i = 0) { } 4) int i ; while( i = 1 + 4) { } 4) int i ; while( i = 5 - 5) { } 5) int i=8; float j=8.0; while(i == j) { } 5) int i=8 ; float j=8.5 ; while(float (i == j)) { } 6) int i=8 ; while( i >=5 && i <= 10 ) { } 6) int i=8 ; while( i >= 1 && i <=5 ) { }

for Loop :-
This is most popular Pre-test loop . It is popular because it provide three benifits to the user . It allow us To
®Initialise the Counter variable .
®Test the condition
®Increment/Decrement the Counter variable .

For this reason , " for " loop is more popular among user .

Syntax :-

for(initialise ; condition ; Increment )
{
statement-block
}

for              ---->  Keyword (Reserve word)
initialise     ---->   here we give Initial Value to the Counter variable
condition   ---->   here we can use Condition or any type valid expression
Increment ---->   here we can Increment or Decrement the Counter variable

Working :- The for loop work as .

Firstly it initialise the counter variable .
The loop check the Condition .
If the condition is true ie. give Non-Zero result , it execute the statement-block , Increment the Counter variable , & repeat the second step .
If the condition is false ie. give Zero as result , it leave the statement-block inside the loop & execute the rest of the instruction .

Þ In for loop we can use it in any way , for leaving the space Blank . BUT the syntax must be same .

for( ; ; )
{
statement-block
}

Þ In for loop we can also use any type of valid expression & the statement-block execute only if the expresssion return a Non-Zero result .

for(initialise ; expression ; increment)
{
statement block
}

 EXPRESSION Non-Zero = TRUE Zero = FALSE 1) for( ; 1 ; ) { } 1) for( ; 0 ; ) { } 2) int i=5 ; for( ; i ; ) { } 2) int i=0 ; for( ; i ; ) { } 3) int i ; for( ; i = 8 ; ) { } 3) int i ; for( ; i = 0 ;) { } 4) int i ; for( ; i = 1 + 4 ; ) { } 4) int i ; for( ; i = 5 - 5 ; ) { } 5) int i=8; float j=8.0; for( ; i == j ;) { } 5) int i=8 ; float j=8.5 ; for( ; float (i == j) ; ) { } 6) int i=8 ; for( ; i >=5 && i <= 10 ; ) { } 6) int i=8 ; for( ; i >= 1 && i <=5 ; ) { }

do while loop :-
This is a Post-test loop ie. In this loop the condition is check after the execution of the statement-block .Due to this feature , The statement-block must execute at-least one time not checking that the condition is true or false .

Syntax :-

do
{
statement-block

}while( condition )

Working :-   The working of " do while " loop is .

Firstly it execute the statement-block .
It check the condition .
If condition give Non-Zero result , it repeat the First step .
I condition give Zero value ie. False , it leave the statement-block and execute the rest  of the instructions .
So it must execute the statement-block at least one time , not seeing that the condition is true or false .
Þ In do-while loop we can use any type of valid expression & the statement-block execute only if the expresssion return a Non-Zero result .
do
{
statement block

}while(expression)

 EXPRESSION Non-Zero = TRUE Zero =FALSE 1) do { }while( 1 ) ; 1) do { }while( 0 ); 2) int i=5 ; do { }while( i ); 2) int i=0 ; do { }while(i) ; 3) int i ; do { }while( i == 8 ); 3) int i ; do { }while(i = 0) ; 4) int i ; do { }while( i = 1 + 4 ) ; 4) int i ; do { }while( i = 5 - 5) ; 5) int i=8; float j=8.0; do { }while( i == j ) ; 5) int i=8 ; float j=8.5 ; do { }while(float (i == j)) ; 6) int i=8 ; do { }while(i >=5 && i <= 10) ; 6) int i=8 ; do { }while( i >= 1 && i <=5 ) ;

COUNTER  VARIABLE :-
Counter Variable is a simple Variable which control that how many time the Loop will execute . The counter variable is Incremented   or Decremented with some fix amount as required .

How to use COUNTER :-

Firstly Declare the Counter_Variable and Initialise it .
Set  appropriate condition according to program need .
Put Increment or Decrement instruction for the counter , in the loop .

Example :-

int i ;                        /*  Declaration of  Counter Variable  */
i = 1 ;                     /*  Initialising Counter  Variable  */
while( i <= 10 )        /*  Condition  */
{
printf("\n %d ", i ) ;
i = i + 1 ;                 /*  Incrementing the Counter Variable  */
}

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