Nested Loops in C Programming

In this post on Nested Loops in C Programming, we will learn how you can use nested for loop, nested while loop, and nested do while loop in C programming.

To understand nested loops, it is essential that you know how to use for, while, and do while first, so if you have not read the tutorials before this, then definitely read them first.

Like we used the if inside the if, i.e. nested if, similarly when we use the loop again inside a loop, we call it a nested loop.

We call the outer loop the outer loop, the loop that is inside the outer loop, we call the inner loop.

Mostly the inner loop is used to run the statements and the outer loop controls how many times the inner loop will run.

You can use any loop of the same or another type as a nested loop inside any for, while, or do while loop.

You can also read: do While Loop In C Programming

for(initialization; condition;update) 
{ 
    // statement of outer loop 

    for(initialization; condition; update) 
    { 
           // statement of inner loop 
    } 

    // statement of outer loop 
}

while(condition)
{
    // statement of outer loop

    while(condition)
    {
           // statement of inner loop

           //Update statement of Inner Loop;
    }

    // statement of outer loop

    // Update statement of lower loop;
}

do
{
    // statement of outer loop

    do
    {

           // statement of inner loop

           // Update statement of inner loop

    }while(condition);

    // statement of outer loop

    // Update statement of outer loop
}while(condition);

while(condition)
{
    // statement of outer loop

    for(initialization; condition; increment/decrement)
    {
          // statement of inner loop

          //Update statement of for loop
    }

    do
    {
          //Statement of do-while loop
          //Update statement of do-while loop
    }

    while(condition);
    // statement of outer loop
    // Update statement of while loop
}

With all the above syntax, you must have got a little idea of ​​nested loops, but to understand nested loops in detail, we will understand nested for loop well and from this you will get to know about nested while loop and nested do while loop.

Step 1: Nested for loop starts with variable initialization of outer loop, then control goes on condition of the outer loop (step 2).

Step 2: If the condition of the outer loop becomes true then the control of the program comes inside the outer loop.

Step 3: Now as you can see in the body of the outer loop we have used a nested loop. Now the statements of the body of this inner loop will be repeated until the condition of the inner loop becomes false.

Step 4: When the condition of the inner loop becomes false then the control of the program will come outside the inner loop but still the control of the program is inside the outer loop.

Step 5: Therefore the control of the program will go to the update of the outer loop where there will be an increment or decrement or any other update process in the value of the variable and then again the control of the program will go to step 2.

After step 2, the control of the program will go to step 3, step 4, and then step 5 and this will continue till the condition of the outer loop becomes false at step 2. 

#include <stdio.h>
int main()
{
    int i,j;
 
    for(i=1;i<=3;i++)
    {
        printf("\nI am Outer Loop : i = %d\n",i);
 
        for(j=1;j<=4;j++)
        {
            printf("I am Inner Loop : i = %d, j = %d\n",i,j);
        }
    }
 
    return 0;
}

I am Outer Loop : i = 1
I am Inner Loop : i = 1, j = 1
I am Inner Loop : i = 1, j = 2
I am Inner Loop : i = 1, j = 3
I am Inner Loop : i = 1, j = 4

I am Outer Loop : i = 2
I am Inner Loop : i = 2, j = 1
I am Inner Loop : i = 2, j = 2
I am Inner Loop : i = 2, j = 3
I am Inner Loop : i = 2, j = 4

I am Outer Loop : i = 3
I am Inner Loop : i = 3, j = 1
I am<strong> </strong>Inner Loop : i = 3, j = 2
I am Inner Loop : i = 3, j = 3
I am Inner Loop : i = 3, j = 4

#include <stdio.h>
int main()
{
    int i,j;
 
    for(i=1;i<=3;i++)
    {
        for(j=1;j<=4;j++)
        {
            printf("%d ",j);
        }
        printf("\n");
    }
 
    return 0;
}

1 2 3 4 
1 2 3 4 
1 2 3 4 
1 2 3 4 

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