Simple C Calculator

/************
Simple C calculato Program by Touhid
Dedicated for Tareq
*************/
#include <stdio.h>
int calc(int x, int y, char o);
int main(void){
    int a,b,sum;  // a for first number , b for second number and sum = a  + b

    char o; //operator

    printf("Enter the first number: ");

    //input for first number
    scanf("%d",&a);
    printf("\nEnter the operator: ");

    // input for the operator
    scanf("%s",&o);

    printf("\nEnter the second number: ");

    // input for the second number
scanf("%d",&b);

    // calculate the result according as character variable "o
switch(o){
case '+':
sum = a + b;
break;
case '-':
sum = a - b;
break;
case '*':
sum = a * b;
break;
case '/':
sum = a / b;
break;
default:
sum = NULL;
}

// display the result
printf("\nTotal is: %d", sum);
getch();
return 0;
}