#include<iostream>
#include<string>
using namespace std;

int test_i = 0;

void foo(){
    cout << test_i << endl;
}

int main(){
    int test_i;
    foo();
    test_i = 1;
    cout << test_i << endl;
    foo();
    return 0;
}

运行结果：

0
1
0