Nested Loops in C
A nested loop means a loop statement inside another loop statement.
- For a nested loop, the inner loop performs all of its iterations for each iteration of the outer loop.
- If the outer loop is running from i = 1 to 5 and the inner loop is running from j = 0 to 3. Then, for each value of the outer loop variable (i), the inner loop will run from j = 0 to 3.
1. Nested for Loops
Nested for loop refers to any type of loop that is defined inside a 'for' loop.
#include <stdio.h>
int main() {
// limit for i
int m = 4;
// limit for j
int n = 5;
// Outer loop
for (int i = 0; i < m; i++) {
printf("i = %d: ", i);
// InnerLoop
for (int j = 0; j < n; j++) {
printf("%d ", i * n + j);
}
printf("\n");
}
return 0;
}
Output
i = 0: 0 1 2 3 4 i = 1: 5 6 7 8 9 i = 2: 10 11 12 13 14 i = 3: 15 16 17 18 19
Below is the equivalent flow diagram for nested 'for' loops:
2. Nested while Loops
A nested while loop refers to any type of loop that is defined inside a 'while' loop.
#include <stdio.h>
int main()
{
int end = 5;
printf("Pattern Printing using Nested While loop");
int i = 1;
while (i <= end) {
printf("\n");
int j = 1;
while (j <= i) {
printf("%d ", j);
j = j + 1;
}
i = i + 1;
}
return 0;
}
Output
Pattern Printing using Nested While loop 1 1 2 1 2 3 1 2 3 4 1 2 3 4 5
Below is the equivalent flow diagram for nested 'while' loops:
3. Nested do-while Loops
A nested do-while loop refers to any type of loop that is defined inside a do-while loop.
#include <stdio.h>
int main()
{
int i = 1;
do
{
int j = 1;
do
{
printf("%d ", j);
j++;
} while (j <= 3);
printf("\n");
i++;
} while (i <= 2);
return 0;
}
Output
1 2 3 1 2 3
Below is the equivalent flow diagram for nested 'do-while' loops:
4. Hybrid Nested Loops
A hybrid loop structure is where any type of loop is nested inside another loop type.
#include <stdio.h>
int main()
{
int i = 1;
while (i <= 2)
{
// Outer while loop
for (int j = 1; j <= 2; j++)
{
// Inner for loop
printf("i = %d, j = %d\n", i, j);
}
i++;
}
return 0;
}
Output
i = 1, j = 1 i = 1, j = 2 i = 2, j = 1 i = 2, j = 2
Break Inside Nested Loops
Whenever we use a break statement inside the nested loops it breaks the innermost loop only and program control goes to the outer loop. Breaking the inner loop does not affects the outer loops.
#include <stdio.h>
int main()
{
int i = 0;
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 3; j++) {
// This inner loop will break when i==3
if (i == 3) {
break;
}
printf("* ");
}
printf("\n");
}
return 0;
}
Output
* * * * * * * * * * * *
In the above program, the first loop will iterate from 0 to 5 but here if i will be equal to 3 it will break and will not print the * as shown in the output.
Continue Inside Nested Loops
Whenever we use a continue statement inside the nested loops it skips the iteration of the innermost loop only. The outer loop remains unaffected.
#include <stdio.h>
int main()
{
int i = 0;
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 3; j++) {
// This inner loop will skip when j==2
if (j==2) {
continue;
}
printf("%d ",j);
}
printf("\n");
}
return 0;
}
Output
0 1 0 1
In the above program, the inner loop will be skipped when j will be equal to 2. The outer loop will remain unaffected.
Uses of Nested Loops
- Printing Patterns: Nested loops are often used to print complex patterns such as printing shapes, grids, or tables.
- Searching and Sorting: Nested loops are used in algorithms that involve searching for or sorting elements like bubble sort, insertion sort, matrix searching etc.
- Multi-Dimensional Data: Nested loops are useful when dealing with multidimensional data structures like 2D or 3D arrays, matrices, list of lists.
- Dynamic Programming: Nested loops are commonly used in dynamic Programming for solving problems like knapsack problem or longest common subsequence.
