I'm trying to build a simple calculator using C and the switch case. If I try to use characters instead of integers, the program doesn't work: it reads what I type into the input buffer and it stores it into the variables, but it doesn't recognize any case. What am I doing wrong? I'm sorry if this question is a duplicate, I tried to search for a solution, but my code is looking fine to me, so I don't understand what is wrong.

#include <stdio.h>
#include <stdlib.h>

int main ()
{
    char s[80], op[80];
    int num1, num2, res;
    

    printf("Please type your operation:\n");
    fgets (s, sizeof(s), stdin); 
    num1 = atoi(s); 
    fgets (op, sizeof(op), stdin);
    fgets (s, sizeof(s), stdin);
    num2 = atoi(s);

    switch (op[80]) {
        case ' ' :
            res = num1   num2;
            printf("%i\n", res);
            break;
        case '*' :
            res = num1 * num2;
            printf("%i\n", res);
            break;
        default:
            return 1;
    }
    return 0;
}

CodePudding user response：

You're reading into op which is a character array of length 80, but then switch-ing on op[80] which is (just) beyond the length of op. Try changing that to op[0] to mean the first character of op.