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

int addition(int a, int b);
int subtraction(int a, int b);
int multiplication(int a, int b);
int division(int a, int b);
int modulo(int a, int b);

int main(void) {

    char selection;

    int a, b, c;

    printf("Please select one of the following operations: \n"
           "a - addition\n"
           "s - subtraction\n"
           "m - multiplication\n"
           "d - division\n"
           "r - modulo\n"
           "Char: ");

    scanf("%c", &selection);

    if(selection == 'a') {
        printf("Enter a number: \n");
        scanf("%d", &a);

        printf("Enter another number: \n");
        scanf("%d", &b);

        c = addition(a ,b);

        printf("%d + %d = %d\n", a, b, c);
    }

    else if(selection == 's') {
        printf("Enter a number: \n");
        scanf("%d", &a);

        printf("Enter another number: \n");
        scanf("%d", &b);

        c = subtraction(a ,b);

        printf("%d - %d = %d\n", a, b, c);
    }

    else if(selection == 'm') {
        printf("Enter a number: \n");
        scanf("%d", &a);

        printf("Enter another number: \n");
        scanf("%d", &b);

        c = multiplication(a ,b);

        printf("%d * %d = %d\n", a, b, c);
    }

    else if(selection == 'd') {
        printf("Enter a number: \n");
        scanf("%d", &a);

        printf("Enter another number: \n");
        scanf("%d", &b);

        c = division(a ,b);

        printf("%d / %d = %d\n", a, b, c);
    }

    else if(selection == 'r') {
        printf("Enter a number: \n");
        scanf("%d", &a);

        printf("Enter another number: \n");
        scanf("%d", &b);

        c = modulo(a ,b);

        printf("%d r %d = %d\n", a, b, c);
    }

    else {
        printf("Wrong choice! Re-run program.\n");
    }

}

int addition(int a, int b) {
    int ans = a + b;
    return ans;
}

int subtraction(int a, int b) {
    int ans = a - b;
    return ans;
}

int multiplication(int a, int b) {
    int ans = a * b;
    return ans;
}

int division(int a, int b) {
    int ans = a / b;
    return ans;
}

int modulo(int a, int b) {
    int ans = a % b;
    return ans;
}