Loops

LOOP:

A loop is a sequence that gets executed several times. The ability to specify repetition of a group of instructions is an important problem-solving tool.

TYPES OF LOOPS:

For loop Statement.
While loop Statement.
Do-while Statement.

for Loop:

The for loop consist of three parts
1- The initialization: Set the loop control variable assignment.
2- The condition: A relational expression that determines when the loop exits.
3-The increment: Defines how the loop control variable changes each time the loop is repeated.

Syntax:

for (initialization expression ; loop repetition condition ; update expression )
{
Statement_Block;
}

INTERPRETATION:

First, the initialization expression is executed.
Then, the loop condition is tested. If it's true, the statement is executed, and the update expression is evaluated.
Then the loop repetition condition is retested.
The statement is repeated as long as the loop condition is true. When this condition is false, the for loop is exited, and the next program statement after the for statement is executed.

While Statement:

This loop is used to repeat a section of code an unknown number of times until a specific condition is met.
WHILE loop and FOR loop can be used interchangeably. But normally FOR loop is used when the exact number of iterations of the loop are known. WHILE loop is used when the number of iterations is not known.

SYNTAX:

while ( loop repetition condition )
{
Statement_Block;
}

INTERPRETATION:

The loop repetition condition (a condition to control the loop process) is tested; if it's true, the statement (loop body) is executed, and the loop condition is retested.
The statement is repeated as long as the loop condition is true. When this condition is false, the while loop is exited and the next program statement after the while statement is executed.

 

Do-While Loop:

Unlike for and while loops, which test the condition at the top of the loop, do while loop checks its condition at the bottom of the loop. This means that it always executes at least once.
This loop executes the loop body again and again as long as condition evaluates to true.

C- SYNTAX:

do
{
Statement_Block;
} while ( loop repetition condition );

INTERPRETATION:

First, the statement is executed.
Then, the loop repetition condition is tested, and if it's true, the statement is repeated and the condition retested. When this condition is false, the loop is exited and the next statement after the do-while is executed.

Implementation of Loops in C:

Q: Write a program to test whether a given number is prime or not.

#include<stdio.h>

int main()
{
 int no,x=1;
 int count=0,y;
 printf("Please enter Number ");
 scanf("%d",&no);
 while (no>=x)
 {
  y=no%x;
  x++;
  if (y==0)
  {
   count=count+1;
  }
 }
 if (count==2)
 {
  printf("\n%d is a Prime number",no);
 }
 else
 {
  printf("\n%d is a Not Prime number",no);
 }
return 0;
}

Q: Write a program to reverse the digits of a number such that 1234 becomes 4321.

#include<stdio.h>

int main()
{
 int no,a;
 int sum=0;
 printf("Please enter Number ");
 scanf("%d",&no);
 a=no;
 do
 { 
  a=no%10;
  sum=(sum*10)+a;
  no=no/10;
 }
 while (no!=0); 
 printf("The reverse number is %d ",sum);
 return 0;
 
 printf("%c",65);
}

Pattern printing Diamond:

#include<stdio.h>

int main()
{
 int x,y,a,b,z;
 for (x=0;x<10;x++)
 {
  for(a=10;a>x;a--)
  {
   printf(" ");
  }
  printf("*");
  
  for (y=0;y<x;y++)
  {
   printf("  ");
   
  }
  printf("*");
  printf("\n");
 }
 
 for (x=0;x<10;x++)
 {
  for(y=0;y<x;y++)
  {
   printf(" ");
  }
  printf("*"); 
  
  for (z=10;z>x+1;z--)
  {
   printf("  ");
  }
  printf("*");
  printf("\n");
 }
 return 0;
}