Once a name has been declared in a scope, that name can be used by scopes nested inside that scope. Names declared in the outer scope can also be redefined in an inner scope

#include <iostream>
// Program for illustration purposes only: It is bad style for a function
// to use a global variable and also define a local variable with the same name
int reused = 42; // reused has global scope
int main()
{
int unique = 0; // unique has block scope
// output #1: uses global reused; prints 42 0
std::cout << reused << " " << unique << std::endl;
int reused = 0; // new, local object named reused hides global reused
// output #2: uses local reused; prints 0 0
std::cout << reused << " " << unique << std::endl;
// output #3: explicitly requests the global reused; prints 42 0
std::cout << ::reused << " " << unique << std::endl;
return 0;
}