These Functions should work but why aren't they? The compiler says Error: too few arguments to function "whatever's inside". I am a beginner to C so forgive my stupidness. I would also like to know what can be in a function.

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

int x;
int y;

int multiply (int x, int y)
{
    printf("()");
    return x*y;
    getchar();
    scanf("%d", &x);
    scanf("%d", &y);
    printf(":\n", multiply(x, y));

}

int add (int x, int y)
{
    printf("()");
    return x+y;
    getchar();
    scanf("%d", &x);
    scanf("%d", &y);
    printf(":\n", add(x, y));
}

int divide (int x, int y)
{
    printf("()");
    return x/y;
    getchar();
    scanf("%d", &x);
    scanf("%d", &y);
    printf(":\n", divide(x, y));
}

int subtract(int x, int y)
{
    printf("()");
    return x-y;
    getchar();
    scanf("%d", &x);
    scanf("%d", &y);
    printf(":\n", divide(x, y));
}

int power(int x, int y)
{
    printf("()");
    pow(x, y);
    getchar();
    scanf("%d", &x);
    scanf("%d", &y);
    printf(":\n", power(x, y));
}

//main code

int main(void)
{
    int option;

    switch (option)
    {
    case 1:
    add();
    break;

    case 2:
    subtract();
    break;

    case 3:
    multiply();
    break;

    case 4:
    divide();
    break;

    case 5:
    power();
    break;

    }
    getchar();
}

You are probably looking for the following code:

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

int multiply (int x, int y)
{
    return x*y;
}

int add (int x, int y)
{
    return x+y;
}

int divide (int x, int y)
{
    return x/y;
}

int subtract(int x, int y)
{
    return x-y;
}

int power(int x, int y)
{
    return pow(x, y);
}

//main code

int main(void)
{
    int option, result, x, y;
    printf("Enter the numbers:\n");
    scanf("%d%d",&x,&y);
    printf("1. Add\n2. Subtract\n3. Multiplu\n4. Divide\n5. Power\nEnter your choice:\t");
    scanf("%d",&option);
    switch (option)
    {
    case 1:
    result = add(x,y);
    break;

    case 2:
    result = subtract(x,y);
    break;

    case 3:
    result = multiply(x,y);
    break;

    case 4:
    result = divide(x,y);
    break;

    case 5:
    result = power(x,y);
    break;

    }
    printf("\nRequired result = %d",result);
    getchar();
}

You might want to include some condition in your code like division by 0 shouldn't be allowed, et cetra.