奇怪的错误-即使我从未更改结果，打印出数组内容也会改变结果

Question

I'm writing a function that fills up three arrays with user input and calculates the average of their values. But I am getting a weird error.

This is so weird. When I comment out this code:

for (int i = 0; i < 5; i++)
    cout << Steve[i] << ",";
cout << endl;

---

#include <iostream>

using namespace std;
void fill_up(int a[], int size);

void fill_up(int a[], int size)
{
    cout << "Enter " << size << " numbers:\n";
    for ( int i = 0; i < size; i++ )
        cin >> a[i];
    size--;
    cout << "The last array index used is " << size << endl;
}
int main()
{
    int Steve[5];
    int George[5];
    int Mary[5];
    cout << "~ Fill up the Steve array ~" << endl;
    fill_up(Steve, 5);
    cout << "~ Fill up the George array ~" << endl;
    fill_up(George, 5);
    cout << "~ Fill up the Mary array ~" << endl;
    fill_up(Mary, 5);

    /*
    for (int i = 0; i < 5; i++)
        cout << Steve[i] << ",";
    cout << endl;
    */

    int SteveSum, GeorgeSum, MarySum = 0;
    double SteveAvg, GeorgeAvg, MaryAvg;
    for(int i = 0; i < 5; i++)
    {
        SteveSum += Steve[i];
        GeorgeSum += George[i];
        MarySum += Mary[i];
    }
    SteveAvg = ((double) SteveSum ) / 5;
    GeorgeAvg = ((double) GeorgeSum ) / 5;
    MaryAvg = ((double) MarySum ) / 5;

    cout << "Steve's average is " << SteveAvg << endl;
    cout << "George's average is " << GeorgeAvg << endl;
    cout << "Mary's average is " << MaryAvg << endl;
}

Here are two screenshots of the code running on command line.

As you can see when I comment out that print array snippet, Steve's average comes out to a weird large number, but when I uncomment that snippet it works fine. What's going on?

Answer 1

Wrong:

int SteveSum, GeorgeSum, MarySum = 0;

Right:

int SteveSum = 0, GeorgeSum = 0, MarySum = 0;