// simple calculator using sscanf and fgets
// gcc -o calc calc.c
//

#include <stdio.h>

// an invalid expression was supplied let the user know
void invalid()
{
    printf("invalid expression\n");

}

int main(int argc, char **argv)
{
    int x, y, z;        // storage for our values
    int line = 0;       // current line number
    char op;        // operator from the user
        char buf[20];
        printf("Press ctrl-c to exit\n");

    // continue processing user input until SIGINT
    while(1)
    {
        line++;             // increment line number
        x = y = z = op = 0;     // reset our storage
        printf("%d> ", line);       // print a REPL prompt to the terminal
                fgets(buf, 20 - 2, stdin);      // fixed the memory error
            sscanf(buf, "%d %c %d", &x, &op, &y); // read the expression from the terminal

        // test that the expression is valid
        if(x < 0 || op == 0 || y < 0)


        {
            // try again
            invalid();
            continue;
        }

        // evaluate the expression based on it's infix operator
        switch(op)
        {
            case '+':
                // add
                z = x + y;
                break;
            case '-':
                // subtract
                z = x - y;
                break;
            case '*':
                // multiply
                z = x * y;
                break;
            case '/':
                // divide
                                if ( y == 0)
                       {
                    // you can't divide by zero.
                    invalid();
                    continue;
               }
                z = x / y;
                            break;
            case '^':
                // xor
                z = x ^ y;
                break;
            default:
                // invalid
                invalid();
                continue;
        }
        // print the result to the terminal
        printf("%d\n", z);
    }
}