for 循环内的条件判断作用域

#include<iostream>
#include<string>
#include<vector>
using namespace std;
string test1() {
    for (int i = 0; i < 5; ++i) {
        if (i==0)
            return "ok";
        return "null";
    }
}
string test2() {
    for (int i = 0; i < 5; ++i) 
        if (i==5)
            return "ok";
        return "null";
}
string test3() {
    for (int i = 0; i < 5; ++i) {
            return "ok";
    }
}
int main() {
    cout << test3();
    system("pause");
}