Loop Control

August 30, 2020

Loop Control

1. The for Loop

The for loop gathers all its loop control elements on the top of the loop.

A for loop can have multiple initialization and update expressions separated by commas.

Syntax:

for(initialization expression(s);test-expression;update expression(s))
{ 
//body of the loop; 
}

//Printing numbers using for loop
#include<stdio.h>
int main(){
  int i;
  for(i=1;i<=5;i++){
    printf("i: %d\n",i);
  }
  return 0;
}

Output:

i: 1
i: 2
i: 3
i: 4
i: 5

2. The while Loop

The while loop evaluates a test-expression before allowing entry into the loop. Syntax:

while(expression)
{
//loop-body; 
}

//Program to find factorial of a number
#include <stdio.h>
int main()
{
    int num,i=1,fact=1;
    printf("Enter a number: ");
    scanf("%d",&num);
    while(i<=num){
        fact = fact * i;
        i++;
    }
    printf("Factorial of %d = %d",num,fact);

    return 0;
}

Output:

Enter a number: 6
Factorial of 6 = 720

3. The do-While Loop

The do-while loop executes at least once when the test-expression is false initially. It executes at least once always as it evaluates the test expression at the end of the loop. Syntax:

do 
{ 
//statement; 
}while(test-expression);

4. Nested Loop

A loop may contain another loop in its body. This type of a loop is called a nested loop.

In a nested loop, the inner loop must terminate before the outer loop terminates.

//Program to print table from 1 to 10
#include<stdio.h>
int main()
{
int i,j;
for(i=1;i<=10;i++){
  {
    for(j=1;j<=10;j++)
      {
        printf("%d\t",i*j);
      }
     printf("\n");
  }
  return 0;
}

/** * C program to print heart star pattern */
#include<stdio.h> 
int main() { 
    int a, b, line = 12; 
  
    for (a = line/2; a <= line; a = a+2) { //for the upper part of the heart
        for (b = 1; b < line-a; b = b+2) //create space before the first peak         
            printf(" "); 
   
        for (b = 1; b <= a; b++) //print the first peak
            printf("*"); 
   
        for (b = 1; b <= line-a; b++) //create space before the first peak
            printf(" "); 
           
        for (b = 1; b <= a-1; b++) //print the second peak
            printf("*"); 
        printf("\n"); 
    } 

    for (a = line; a >= 0; a--) { //the base of the heart is inverted triangle
        for (b = a; b < line; b++) //generate space before triangle
            printf(" "); 
  
        for (b = 1; b <= ((a * 2) - 1); b++) //print the triangle
            printf("*"); 
  
        printf("\n");   
    } 
}

Output:

   ******      *****
  ********    *******
 **********  *********
***********************
***********************
 *********************
  *******************
   *****************
    ***************
     *************
      ***********
       *********
        *******
         *****
          ***
           *

5.Infinite Loop

A loop that never ends. A loop becomes infinite loop if a condition never becomes false. You can make an endless loop by leaving the conditional expression empty.

#include <stdio.h>
int main()
{
  int i = 1;
  for( ; ; )
    {
      printf("%d\n",i);
    }
return 0;
}