QUESTION 07 · Selection

What is a nested if statement?

2 marks

Answer

A nested if is an if statement placed inside another if or else branch.

The inner decision is reached only when its enclosing path is selected.
Use braces to make the matching of if and else clear.

Explain nested if statements with an example.

5 marks

Answer in brief

A nested if statement places one decision inside another decision. It is useful when a second test is needed only after a first test.

Syntax

if (condition1) {
    if (condition2) {
        /* both conditions true */
    } else {
        /* first true, second false */
    }
} else {
    /* first condition false */
}

Example: largest of three values

First compare a with b. If a >= b, compare a with c; the larger of a and c is the maximum. Otherwise, b is larger than a, so compare b with c. This arrangement checks only the part needed for the selected path.

Worked case

For a = 12, b = 7 and c = 20, a >= b is true. The inner test a >= c is false. Therefore c, which is 20, is selected. For equal maximum values, using >= still selects a correct maximum value.

Matching else

Without braces, an else belongs to the nearest earlier unmatched if. Indentation alone does not change this rule. Braces are the safest way to express the intended nesting. Very deep nesting can be difficult to read; consider an else-if ladder or a simpler condition when suitable.

Complexity

The maximum-of-three example makes a fixed number of comparisons and uses a fixed number of variables. Its time and auxiliary space are both O(1). The result does not require sorting the three numbers.

C program and output

Download .c Open compiler

/* CodeBhavya | PPS AR25 | Learning example */
#include <stdio.h>
int main(void)
{
    int a = 12, b = 7, c = 20, maximum;
    if (a >= b) {
        if (a >= c) { maximum = a; }
        else { maximum = c; }
    } else {
        if (b >= c) { maximum = b; }
        else { maximum = c; }
    }
    printf("Maximum = %d\n", maximum);
    return 0;
}

Sample input and output

This example uses values already written in the program.

Output

Maximum = 20