PeakA TEACHING EXAMPLE · C PROGRAMMING
A calculator you can explain.
Two numbers, one operation, a result. Try the behavior here, then build the C program on your computer.
Try the interaction
This browser demo uses JavaScript to show the expected behavior. The C source below runs separately with a compiler.
BUILD IT YOURSELF
Understand each step.
- Read two numbers and an operator. Reject input that does not match.
- Choose the operation with a switch statement.
- Handle division by zero before performing division.
- Print the result and test all four operations.
Save as calculator.c. Build: gcc -Wall -Wextra -pedantic calculator.c -o calculator. Run ./calculator, or calculator.exe on Windows.
Read the C source
/* Local teaching example: gcc -Wall -Wextra -pedantic calculator.c -o calculator */
#include <stdio.h>
#include <math.h>
int main(void) {
double first, second, result;
char operation;
printf("Enter an expression, for example 12 + 8: ");
if (scanf("%lf %c %lf", &first, &operation, &second) != 3 ||
!isfinite(first) || !isfinite(second)) {
fprintf(stderr, "Enter two finite numbers and an operator.\n");
return 1;
}
switch (operation) {
case '+': result = first + second; break;
case '-': result = first - second; break;
case '*': result = first * second; break;
case '/':
if (second == 0.0) {
fprintf(stderr, "Cannot divide by zero.\n");
return 1;
}
result = first / second;
break;
default:
fprintf(stderr, "Supported operators: + - * /\n");
return 1;
}
if (!isfinite(result)) {
fprintf(stderr, "Result is outside the supported range.\n");
return 1;
}
printf("Result: %.12g\n", result);
return 0;
}