Menu loop
- C course
- Beginner
- Lesson 22/116
- 6 min
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.
Practice 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.
Starter code
#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");
printf("%d\n", add(5, 3));
printf("%d\n", subtract(5, 3));
printf("%d\n", multiply(5, 3));
printf("%d", divide(6, 3));
return 0;
}Sample 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;
}Expected output
Calculator 8
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Best loop for a menu?
- for
- do-while
- while Correct answer
- foreach
Explanation: while loops as long as the condition holds; it suits a menu.
2 Loop condition
while (____) { ... }while (choice != 0) { ... }Explanation: choice != 0 keeps the loop running until choice becomes 0.
3 What does break do in switch?
- Starts the loop
- Falls to next case
- Goes to default
- Exits the switch Correct answer
Explanation: break exits the switch and prevents falling to the next case.