for（x：y）循环在c ++中无法正常工作

Question

I've tried 2 different for loops, 1 of which works but the other doesn't appear to. output of the first for loop: 2 3 4 5 5, output of the second for loop: 1 2 3 4 5.

#include <iostream>
int main() 
{
    int arr[5] = {1,2,3,4,5};
    for (int y : arr) std::cout << arr[y] << std::endl;
    std::cout << "---------" << std::endl;
    for (int i = 0; i<5;i++){
        std::cout << arr[i] << std::endl;
    }
    return 0;
}

Answer 1

The first loop is a range-based loop, used as a more readable equivalent to the traditional for loop operating over a range of values, such as all elements in a container ( https://en.cppreference.com/w/cpp/language/range-for )

It is similar to a java or C# foreach style loop.

In this kind of loop, the values that y takes are the values of the elements in the array themselves ( 1,2,3,4,5), not the indexes (0,1,2...) so you don't need to print arr[y] , just print y itself

For example, both the loops in the following code will print 10,20,30,40,50

#include <iostream>
int main() 
{
    int arr[5] = {10,20,30,40,50};
    for (int y : arr) std::cout << y << std::endl;
    std::cout << "---------" << std::endl;
    for (int i = 0; i<5;i++){
        std::cout << arr[i] << std::endl;
    }
    return 0;
}