Why x and y occur twice

Question

#include <stdio.h>

int sum_up (int x, int y);

int main() {
int x, y, result;

x = 3;
y = 12;
result = sum_up(x, y);
printf("%d + %d = %d", x, y, result);

return 0;
}

int sum_up (int x, int y) {
x += y;
return(x);
}

Why x and y occur twice? I mean one before main() an the other after it. how do we know which one is being called?
thank you in advance ^^

Answer 1

In wich and every function, you need to define variables explicitly , therefore in main ()
x and y is defined for 1st time and. In function. sum_up() it is defined for 2nd time...

Answer 2

These variables defined under any specific function are called local variables and to avoid this situation you can have Global variables..........