How to read * from command line in C

Question

I'll go straight to the point. This is my code, and I want to read the '*' char from command line parameter, but it's not working properly. I hope you can explain me what I'm doing wrong.

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

int sum(int, int);
int rest(int, int);
int division(int, int);
int mult(int, int);
int module(int, int);

int main(int argc, char **argv){

    char operator;
    int number1;
    int number2;
    int result;

    if(argc != 4){
        printf("Wrong parameter quantity (%d of 3 needed)\n", argc-1);
        return -1;
    }

    number1 = atoi(argv[1]);
    operator = *argv[2];
    number2 = atoi(argv[3]);

    switch(operator){
        case '+':
                result = sum(number1, number2);
                printf("%d %c %d = %d\n", number1, operator, number2, result);
                break;
        case '-':
                result = rest(number1, number2);
                printf("%d %c %d = %d\n", number1, operator, number2, result);
                break;
        case '/':
                result = division(number1, number2);
                printf("%d %c %d = %d\n", number1, operator, number2, result);
                break;
        case '*':
                result = mult(number1, number2);
                printf("%d %c %d = %d\n", number1, operator, number2, result);
                break;
        case '%':
                result = module(number1, number2);
                printf("%d %c %d = %d\n", number1, operator, number2, result);
                break;
        default:
                printf("Error. Wrong operator inserted (%d, %c)\n", operator, operator);
                return -2;
    }

    return 0;
}

int sum(number1, number2){
    return number1 + number2;
}

int rest(number1, number2){
    return number1 - number2;
}

int division(number1, number2){
    return number1 / number2;
}

int mult(number1, number2){
    return number1 * number2;
}

int module(number1, number2){
    return number1 % number2;
}

I know my mistake is en this line operator = *argv[2]; but I don't know what happens when the '*' char is passed through command line parameter. For all other symbols (+, -, /, %) everything works fine. I'm coding this in Ubuntu and compiling in command line with gcc.

Answer 1

The problem isn't in your program. It's how you're calling it.

The UNIX/Linux shell automatically expands * on the command line to all files in the current directory. To prevent that, you need to quote it.

So instead of doing this

./prog 3 * 4

Do this:

./prod 3 "*" 4

Or this:

./prod 3 \* 4