Menu loop

Write a menu loop with switch-case.

while and switch for a menu

So far the calculator ran all operations one after another. A real calculator lets the user pick an operation from a menu. We use a while loop and a switch statement:

int choice = 1;
while (choice != 0) {
    switch (choice) {
        case 1: ... break;
        case 2: ... break;
        default: break;
    }
    choice = 0;
}

while runs the loop, switch executes the branch for the choice.

The switch statement

The switch statement runs different branches based on a variable's value:

switch (choice) {
    case 1: add(...); break;
    case 2: subtract(...); break;
    default: break;
}

Each case needs a break at the end; otherwise execution falls through to the next case. default runs when no case matches.

Exercise Add a menu loop

Modify main in the code below: replace the printf calls with a while loop and switch. Start with int choice = 1;, include case 1: printf("%d\n", add(5, 3)); break; and case 2: printf("%d\n", subtract(5, 3)); break;, plus default: break; and choice = 0; at the end. Keep printf("Calculator\n"); as the header.

Show example solution

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int subtract(int a, int b) {
    return a - b;
}

int multiply(int a, int b) {
    return a * b;
}

int divide(int a, int b) {
    if (b == 0) return 0;
    return a / b;
}

int main(void) {
    printf("Calculator\n");
    int choice = 1;
    while (choice != 0) {
        switch (choice) {
            case 1: printf("%d\n", add(5, 3)); break;
            case 2: printf("%d\n", subtract(5, 3)); break;
            default: break;
        }
        choice = 0;
    }
    return 0;
}

Test yourself

Best loop for a menu?
- for
- do-while
- while
- foreach
Show answer

while — while loops as long as the condition holds; it suits a menu.

Loop condition

while (____) { ... }

Show answer

while (choice != 0) { ... }

What does break do in switch?
- Starts the loop
- Falls to next case
- Goes to default
- Exits the switch
Show answer

Exits the switch — break exits the switch and prevents falling to the next case.

Next lesson: Putting it together

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