为什么C++中的foreach不能遍历第一个元素？

Question

In foreach loop, it seems the first element is not traversed and the 6th element num[5] is traversed which is undefined.

#include<iostream>
using namespace std;
int num[5];
int main() {
    for (int i = 0; i < 5; i++) num[i] = i + 1;
    for (auto i : num) cout << num[i] << " ";
    return 0;
}

expected output: 1,2,3,4,5

output: 2,3,4,5,0

Answer 1

Because i is not an index, but the value, you should replace:

for (auto i:num)cout<<num[i]<<" ";

with

for (auto i:num)cout<< i <<" ";

Then you get the proper output 1 2 3 4 5

Answer 2

for (int i=0;i<5;i++)num[i]=i+1;

Loads the num variable like [0] = 1 , [1] = 2 ... [4] = 5

for (auto i:num)cout<<num[i]<<" ";

This actually goes through the values in num , not the indexes, so what you have here is printing num[1] , num[2] ... num[5] ( num[5] is undefined behavior by the way)