What is Nested do while in C?

A nested do while loop in C is a loop that is enclosed within another do while loop. It is a loop inside a loop. In this loop structure, the inner loop executes multiple times for each iteration of the outer loop.

We use a nested do while loop in C to perform a specific task repeatedly. We can use it when we need to iterate through a set of data multiple times, with each iteration involving a different set of operations.

Syntax:

do {
  // Outer loop statements
  do {
    // Inner loop statements
  } while (condition);
} while (condition);

Here, the inner loop is executed until the given condition is true. Then, the outer loop is executed until its condition becomes false.

Examples of Nested do while loop in C:

1. Printing Multiplication Table from 1 to 5

#include <stdio.h>

int main() {
   int i = 1;
   int j;

   do {
      j = 1;
      do {
         printf("%d * %d = %d\n", i, j, i*j);
         j++;
      } while(j <= 10);
      i++;
   } while(i <= 5);

   return 0;
}

Output:

1 * 1 = 1
1 * 2 = 2
1 * 3 = 3
...
...
...
5 * 8 = 40
5 * 9 = 45
5 * 10 = 50

Explanation:

In above example, the nested do while loop is used to print the multiplication table of numbers from 1 to 5. The outer loop runs from 1 to 5 and the inner loop runs from 1 to 10. The output displays the result of each multiplication table.

2. Printing a matrix based on the size given by user

#include <stdio.h>

int main() {
   int i = 1;
   int j = 1;
   int n;

   printf("Enter the value of n: ");
scanf("%d", &n);

do {
do {
if(i == j) {
printf("%d ", i);
} else {
printf("0 ");
}
j++;
} while(j <= n);
printf("\n");
i++;
j = 1;
} while(i <= n);

return 0;
}

Output:

Enter the value ofn: 6
1 0 0 0 0 0 
0 2 0 0 0 0 
0 0 3 0 0 0 
0 0 0 4 0 0 
0 0 0 0 5 0 
0 0 0 0 0 6 

Explanation:

In above example, the nested do while loop is used to print a diagonal matrix of numbers from 1 to n. The outer loop runs from 1 to n and the inner loop runs from 1 to n. The output displays a matrix with all values set to 0, except for the diagonal, which is set to the corresponding number.

3. Printing a Box of Asterisks

#include <stdio.h>
int main() {
   int i = 1, j = 1, n = 5;
   do {
      do {
         if(j==1 || j==n || i==1 || i==n) {
            printf("* ");
         } else {
            printf("  ");
         }
         j++;
      } while(j <= n);
      printf("\n");
      i++;
      j = 1;
   } while(i <= n);
   return 0;
}

Output:

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

Explanation:

In above example, the nested do-while loop is used to print a hollow square of asterisks with sides of length n. The outer loop runs from 1 to n and the inner loop runs from 1 to n as well. The if-else statement is used to print an asterisk (*) if the current iteration is on the border of the square or to print a space ( ) if it is inside the square.

4. Some kind of sparkle

#include <stdio.h>

int main() {
    int i = 1, j = 1, k = 1, n = 5;
    do {
        do {
            k = (i + j) % 2;
            if(k == 0) {
                printf("* ");
            }
            else {
                printf("# ");
            }
            j++;
        } while(j <= i);
        printf("\n");
        i++;
        j = 1;
    } while(i <= n);
    return 0;
}

Output:

* 
# * 
* # * 
# * # * 
* # * # * 

Explanation:

In above example, the nested do-while loop is used to print a triangular pattern of alternating asterisks (*) and hashes (#) with a base of length n. The outer loop runs from 1 to n, and the inner loop runs from 1 to i. The variable k is used to keep track of whether an asterisk or hash should be printed at each iteration. The output displays the triangular pattern of alternating asterisks and hashes with a base of length 5.

Rules to follow when using nested do while loop in C:

1. Ensure that the loop conditions are set correctly for both the outer and inner loops.
2. Use appropriate variables and expressions within the loop.
3. Ensure that the inner loop is properly nested within the outer loop.
4. Make sure to use proper indentation to make the code more readable.

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