How to use function parameters and arguments in C Language

#include <stdio.h>
void func(int a, int b);
int main()
{
    int x = 10, y = 20;
    func(x, y);
    printf("x = %d, y = %d\n", x, y);
    return 0;
}
void func(int a, int b)
{
    a++;
    b--;
    printf("a = %d, b = %d\n", a, b);
}

a = 11, b = 19
x = 10, y = 20