while loop

It is often the case in programming that we want to do something a fixed number of times. Perhaps we want to calculate gross salaries, or convert temperatures form centigrade to Fahrenheit for 20 different cities. The while loop is ideally suited f or such cases.

Syntax of using while loop:

initialise loop counter

while(valid condition)

{

  statement1;

  statement2;

  statement3;

  statement4;

  increment or decrement loop counter;

}

some basic rule of while loop:

• The statements within the while loop would keep in getting executed till the condition being tested remains true. When the condition becomes false, the control passes to the first statement that follows the body of the while loop.

• The condition being tested may use relational or logical operators as shown in the following examples:
  while(x<=20)
  while(x>=20 && x<=50)
  while(x>=10 || (i>=10 && i<=20)||y==15)
• Almost always, the while must test a condition that will eventually become false, otherwise the loop would be executed forever,indefinitely.
• It is not necessary that a loop counter must only be an int. It can even be a float.
• Example of while loop:

#include<stdio.h>

#include<conio.h>

void main()

{

 int i=1;

 while(i<=5)

 {

  printf("%d\n",i);

  i=i+1;  //i++;

 }

 getch();

}

       Output of above program:

1

2

3

4

5

Nested while loop

One or more loop which require execute again and again then these loop and loops place in separate block is known as nested loop.
Example of nested while loop:

/*demonstration of nested while loop*/

#include<stdio.h>

#include<conio.h>

void main()

{

 int r,c,s;
 clrscr();
 r=1;

 while(r<=5)  /*outer loop*/

 {
  c=1;
  while(c<=2)  /*inner loop*/
  {
   s=r+c;
   printf("r=%d c=%d sum=%d\n",r,c,s);
   c++;
  }
  printf("\n");
  r++;
 }
 getch();
}

         Output of above program:

r=1 c=1 sum=2

r=1 c=2 sum=3

r=2 c=1 sum=3

r=2 c=2 sum=4

r=3 c=1 sum=4

r=3 c=2 sum=5

r=4 c=1 sum=5

r=4 c=2 sum=6

r=5 c=1 sum=6

r=5 c=2 sum=7

Looping concept

The program that we have developed so far used either a sequential or a decision control instruction.

The versatility of the computer lies in its ability to perform a set of instructions repeatedly. This involves repeating some portion of the program either a specified number of times or until a particular condition is being satisfied. This repetitive operation is done through a loop control instruction.
Loops can be created to executed a block of code for a fixed number of times. Alternatively, loops can be created to repetitively execute a block of code until a Boolean condition changes state.
For instance, the loop may continue until a condition changes from false to true, or from true to false. In this case, the block o code being executed must update the condition being tested in order for the loop to terminate at some point. If the test condition is not modified somehow within the loop, the loop will never terminate. This created a programming bug known as an infinite loop.

There are three method by way to which we can repeat a part of a program. They are:

1. Using a for statement
2. using a while statement
3. Using a do-while statement