Chapter 4 Loop Control Instruction

Why loops

Sometimes we want our programs to execute a few sets of instructions over and over again for ex. printing 1 to 100, the first 100 even number, etc.

Hence Loops make it easy for programmers to tell the computer that a given set of instructions must be executed repeatedly.

Types of loops:-

Primarily, there are three types of loops in C language:

1. While loop 

2. do-while loop

3. for-loop

We will look into this one by one

while loop

while(Condition is true) {

//  code

//code                                         =>  The block keeps executing as long as the condition is true

}

An example

int i=0

while (i<10)

printf ("The value of i is %d",i); i++;

NOTE: If the condition never becomes false, the while loop keeps getting executed. Such a Loop is known as an infinite loop.

Increament and decreament operators

i++ ----> i is decreased by 1.

i--  -----> i is decreased by 1

printf ("--i - %d",--i);

 This first documents i and then print it

printf ("i-- =%d",i)

This first print i and then decrement it

*         +++ operator doesn't exist 

*          += is compound assignment operator just like -=, +=, /=,&=

 do-while loop

The syntax of do-while loop looks like this

do{

//code;

//code;

}while(Condition)

 do-while loop works very similar to while loop.

while---> check the condition & then execute the code 

do-while ---> Executes the code & then checks the code

Do-while loop= while loop which executes at least once

for loop

The syntax of the for while loop like this;

for (initialize; test; increment or decrement)

{

//code;

//code;

//code; 

}

Initialize -->

Setting a loop counter to an initial value 

Test ---> Checking a condition

Increment --> updating the loop counter

An Example:

for (i=0; i<3; i++){

printf("%d",i);

printf("\n");

}

Output:

0

1

2

A case of decrement for loop

for (i=5; i, i--)

printf("%d\n",i);

This for loop will keep on running until i become 0

The loop runs in the following steps :

1. "i" is initialized to 5

2. The condition "i" is tested

3. The code is executed

4. "i" is decremented

5. Condition "i" is checked 2 code is executed if its not 0

6. & so on until i is non 0

The Break statement in C

The break statement is used to exit the loop irrespective of whether the condition is true or false.

Whenever a "break" is encountered inside the loop .

The control is sent outside the loop

 Lets us see with the help of an example

for(i=0, i<1000; i++){

printf("%d\n",i);

if (i==5){

break;

}

}

Output:-

0

1

2

3

4

5

and not 0 to 1000

 The Continue statement in C

 The continue statement is used to immediately move to the next iteration of the loop.

The control is taken to the next iteration thus, skipping everything below "continue" inside the loop for that iteration

Let us look at an example

int skip =5;

int i=0;

while (i<10){

if (i=skip)

continue;                  output =5

else

printf("%d",i);

} and not 0.....9

NOTES: 

1. sometimes the name of the variable might not indicate

the behavior of the program.

2. break statement completely exists the loop.

3. continue statement skips the particular iteration of the loop