[Dev-C++] Memory Error in simple array sort

[Opacki, J. <Jos...@ng...>]

When I run the program below, I am getting a memory error:

The instruction ...referenced memory...could not be "read".

I don't exactly don't know what is going on hear, so I thoughI could reach
out to the experts and ask.  

The program asks for a list of integers and inputs them into an array.  You
end the list of integers with a negative number, then the app sorts it and
redisplays your input to you lowest to greatest.  When ran I got the error
above and it crashed.  I then put the sytem("pause") statement in and it ran
fine.  After it paused, then it crashed.

Here is the code:

// array sort demonstration
#include <iostream>
#include <cstdlib>

void fillArray(int a[], int size, int& numberUsed);
/*
    numberUsed is the number of values stored in a.  a[0] through
a[numberUsed - 1]
    have been filled with nonnegative integers read from the keyboard
*/

void sort(int a[], int numberUsed);
/*
    the values of a[0] through a[numberUsed - 1] have been rearranged so
that
    a[0] <= a[1] <= a[2] ... a[numberUsed - 1]
*/

void swapValues(int& v1, int& v2);
// interchanges the values of v1 and v2

int indexSmallest(const int a[], int startIndex, int numberUsed);
/*
    returns the index of i such that a[i] is the smallest of the values
    a[startIndex, a[startIndex + 1] ..., a[numberUsed - 1]
*/

int main()
{
    using namespace std;
    
    cout << "This program sorts numbers from lowest to highest." << endl;
    
    int sampleArray[1], numberUsed;
    
    fillArray(sampleArray, 10, numberUsed);
    sort(sampleArray, numberUsed);
    
    cout << "In sorted order the numbers are: " << endl;
    
    for ( int index = 0; index < numberUsed; index++ )
    {
        cout << sampleArray[index] << " ";
    }
    
    cout << endl;
    
    system("PAUSE");
    return 0;
}

void fillArray(int a[], int size, int& numberUsed)
{
    using namespace std;
    
    cout << "Enter up to " << size << " nonnegative whole number.\n"
         << "Mark the end of the list with a negative number.\n";

    int next, index = 0;
    cin >> next;
    
    while ( (next >= 0) && (index < size) )
    {
        a[index] = next;
        index++;
        cin >> next;
    }
    
    numberUsed = index;
}

void sort(int a[], int numberUsed)
{
    int index_Smallest;
    
    for ( int index = 0; index < numberUsed - 1; index++ )
    { // place the correct value in a[index]
        index_Smallest = indexSmallest(a, index, numberUsed);
        swapValues(a[index], a[index_Smallest]);
        // a[0] <= a[1] <= ... <= a[index] are the smallest of the original
array
        // elements.  The rest of the lements are in the remaining
positions.
    }
}

void swapValues(int& v1, int& v2)
{
    int temp;
    temp = v1;
    v1 = v2;
    v2 = temp;
}

int indexSmallest(const int a[], int startIndex, int numberUsed)
{
    int min = a[startIndex], indexMin = startIndex;
    
    for ( int index = startIndex + 1; index < numberUsed; index++ )
    {
        if ( a[index] < min ) // change to > to change sort arrangement
        {
            min = a[index];
            indexMin = index;
            // min is the smallest of a[startIndex] through a[index]
        }
    }
    
    return indexMin;
}