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Decisions with if and switch

Choose between paths with if, else if, else and switch.

An if statement checks a condition in round brackets. If the condition is true (any non-zero value), the block in curly braces runs.

C
Open in playground
#include <stdio.h>

int main(void) {
    int battery = 15;

    if (battery < 20) {
        printf("Battery low: %d%%\n", battery);
    } else {
        printf("Battery fine.\n");
    }
    return 0;
}
Output
Battery low: 15%
Startbattery = 15battery < 20?YesNoPrint "Battery low"Print "Battery fine."return 0
How the battery check above runs

else if chains

Conditions are tested from top to bottom, and only the first matching block runs.

C
Open in playground
#include <stdio.h>

int main(void) {
    int hour = 14;

    if (hour < 12) {
        printf("Good morning\n");
    } else if (hour < 17) {
        printf("Good afternoon\n");
    } else {
        printf("Good evening\n");
    }
    return 0;
}
Output
Good afternoon

Use && for "and", || for "or" and ! for "not" when you need to combine conditions.

switch

When you compare one value against many fixed options, switch can be clearer than a long else if chain. Each case needs a break, otherwise execution "falls through" into the next case.

C
Open in playground
#include <stdio.h>

int main(void) {
    int day = 3;

    switch (day) {
        case 1: printf("Monday\n"); break;
        case 2: printf("Tuesday\n"); break;
        case 3: printf("Wednesday\n"); break;
        default: printf("Another day\n");
    }
    return 0;
}
Output
Wednesday

GATE-style practice questions

GATE-styleMCQ · one correct answer

What does the following program print?

#include <stdio.h>
int main(void) {
    int x = 3;
    switch (x) {
        case 1: printf("one ");
        case 3: printf("three ");
        case 4: printf("four ");
        default: printf("other ");
        case 5: printf("five ");
    }
    printf("\n");
    return 0;
}
Show answer and explanationAnswer: C

There are no break statements, so after jumping to case 3 execution falls through every following label, including default and case 5, to the end of the switch.

GATE-styleMCQ · one correct answer

What does the following program print?

#include <stdio.h>
int main(void) {
    int a = 5;
    if (a = 0)
        printf("zero ");
    else
        printf("nonzero ");
    printf("%d\n", a);
    return 0;
}
Show answer and explanationAnswer: B

a = 0 is an assignment, not a comparison. It sets a to 0, and the value of the expression is 0, which is false, so the else branch runs. a is now 0.

GATE-styleMCQ · one correct answer

What does the following program print?

#include <stdio.h>
int main(void) {
    int i = 2, j = 0;
    if (i > 1)
        if (j > 0)
            printf("A\n");
    else
        printf("B\n");
    return 0;
}
Show answer and explanationAnswer: B

This is the "dangling else": an else always pairs with the nearest unmatched if, regardless of indentation. So the else belongs to if (j > 0). i > 1 is true and j > 0 is false, so it prints B.