QUESTION 23 · Loops

What is a nested loop?

2 marks

Answer

A nested loop is a loop placed inside the body of another loop.

For every outer iteration, the inner loop runs according to its own control expressions.
A rectangular pattern with r rows and c columns prints r × c items.

Explain nested loops with a rectangular output example.

5 marks

Answer in brief

Nested loops repeat one loop inside another. They are useful for rows and columns, tables and repeated comparisons.

Working

The outer loop selects a row.
For that row, the inner loop processes every required column.
After the inner loop ends, the outer loop moves to the next row.

Example trace

The outer loop runs for rows 1 and 2. For each row, the inner loop runs for columns 1, 2 and 3, printing a star each time. A newline is printed after the inner loop so that each outer iteration produces a separate row. Resetting the inner counter at the beginning of its for loop makes all three columns print on every row.

Common mistakes

Printing the newline inside the inner loop puts each star on a different line. Failing to reset an inner counter can cause later rows to print nothing. Use different counter names, such as row and col, so that updating one loop does not accidentally change the other.

Time complexity

For r outer iterations and c inner iterations each time, the body runs r × c times, giving O(rc) time. If both dimensions equal n, this becomes O(n²). Not every nested loop is quadratic: the limits and total number of executions determine the result. This fixed 2-by-3 sample has six star-print operations.

Space complexity

Only two counters are stored in this example. No array grows with the output size, so auxiliary space is O(1). Printed output itself is not counted as working memory.

C program and output

Download .c Open compiler

/* CodeBhavya | PPS AR25 | Learning example */
#include <stdio.h>
int main(void)
{
    for (int row = 1; row <= 2; ++row) {
        for (int col = 1; col <= 3; ++col) {
            putchar('*');
        }
        putchar('\n');
    }
    return 0;
}

Sample input and output

This example uses values already written in the program.

Output

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