Can someone explain to me this C++ array?

Question

#include <iostream>
using namespace std;
int main()
{
    int arr1[4];
    int arr2[4];
    for (int i = 0;i<=4;i++)
    {
        cin>>arr1[i];
        arr2[i]=arr1[i];
    }
    for(int j = 0;j<=4;j++)
    {
        cout<<arr1[j]<<" ";
        cout<<endl;
    }
    system("PAUSE");
    return EXIT_SUCCESS;
}

Outcome:

Can someone explain to me why arr[0] = 5 ? I cant figure it out.

Answer 1

You accessed out of bounds when i=4 . arr1 and arr2 have only 4 elements. ie arr1[0], arr1[1], arr1[2], arr1[3] and arr2[0], arr2[1], arr2[2], arr2[3] .

Your compiler may assigned arr1 just after arr2 , and accidentaly arr2 + 4 had the same address as arr1 , so the access to arr2[4] wrote the value to arr1[0] .