Nested for loop

Nested means that there is a loop within a loop. A nested loop is executed, essentially, from the inside out.

• Each loop is like a layer and has its own counter variable, its own loop expression and its own loop body.
• In a nested loop, for each value of the outermost counter variable, the complete inner loop will be executed once.

 for (i = 1; i <= 4; i++)
 {   // outer loop
       for (j = 1; j <= 5; j+=2)
       {    // inner loop
            k = i + j;  
            printf(“i=%d, j=%d, k=%d”, i, j, k);
       }
} 

i is the outer loop counter and j is the inner loop counter. The outer loop is executed 4 times, when i =1,2,3, and 4. For each i value the inner loop is executed three times. Since j=1,3, and 5 the inner loop is executed 4*3 or 12 times.

Output is:

 i=1,   j=1,   k=2
 i=1,   j=3,   k=4
 i=1,   j=5,   k=6
 i=2,   j=1,   k=3
 i=2,   j=3,   k=5
 i=2,   j=5,   k=7
 i=3,   j=1,   k=4
 i=3,   j=3,   k=6
 i=3,   j=5,   k=8
 i=4,   j=1,   k=5
 i=4,   j=3,   k=7
 i=4,   j=5,   k=9 

General Form of Nested For Loop

for (loop1_exprs)
{
     loop_body_1a  
     for (loop2_exprs)
     {
           loop_body_2
     }
     loop_body_1b
} 

How many nests can be used for nested for loops?

Ans:   Most compilers allow 15 nesting levels.

For Loop Nesting Patterns

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