In the following code, where are variables b$,$ c$,$ and d stored?

#include

using namespace std;

int a $=10$;

int Add$($int x$,$ int y$)$

$\{$

int b;

b $=$ x $+$ y;

return b;

$\}$

int main$()$

$\{$

int c;

c $=20$;

int d;

d $=$ Add$($a$,$ c$)$;

cout $<<$ d;

return $0$;

$\}$