Bubble Sort returning different results with same input (not out of bounds error based on trace)

Question

I am having an interesting problem that I can't seem to suss out while working on a bubble sort problem. Take in up to 25 integers and sort them from lowest to highest value and reprint the array. This is the code I have written up that logically works on paper:

#include <iostream>

void bubbleSort (int unsorted[25], int sorted[25], int numItems);
void getInput   (int unsorted[25], int toSort[25], int& numItems);
void printArray (int toPrint[25], int& numItems);

int main () {
  int numItems = 25;
  int unsorted[25];
  int sorted[25];

  getInput(unsorted, sorted, numItems);
  printArray(unsorted, numItems);

  bubbleSort(unsorted, sorted, numItems);

  printArray(sorted, numItems);

  return 0;
}

void bubbleSort (int unsorted[25], int sorted[25], int numItems) {
  int temp;
  for (int i = 0; i < numItems; i++)
    for (int j = 0; j < numItems - i; j++)
      if (sorted[j] > sorted[j+1]) {
        temp = sorted[j];
        sorted[j] = sorted[j+1];
        sorted[j+1] = temp;
      }
}

void getInput (int unsorted[25], int toSort[25], int& numItems) {
  int val;
  cout << "Please enter up to 25 integers, one at a time\n"
       << "If less than 25 are to be added, enter '-999' to stop\n";

  for (int i = 0; i < 25; i++) {
    cin >> val;
    if (val == -999) {
      numItems = i;
      break;
    }
    unsorted[i] = val;
    toSort[i]   = val;
  }
  cout << "\nUser input complete\n";
} 

void printArray (int toPrint[25], int& numItems) {
  for (int i = 0; i < numItems; i++)
    cout << " [" << toPrint[i] << "] ";
  cout << endl;
}

The problem I am experiencing is that given the same input, in my case I am using [3, 2, 4, 1, 5] as it was what initially tipped me off to the bug, I can get different output. specifically one of these two with seemingly no rhyme or reason that I can see :

User input complete
[3]  [2]  [4]  [1]  [5] -> entered numbers

[0]  [1]  [2]  [3]  [4] -> sorted numbers

or :

User input complete
[3]  [2]  [4]  [1]  [5] -> entered numbers

[1]  [2]  [3]  [4]  [5] -> sorted numbers

Both outputs are from the same compiled program and seems to just randomly decide if it'll chop off my highest value and replace it with a 0. I know it isn't actually random but I can't figure what is causing it for the life of me.

Answer 1

In your sort function, change for (int j = 0; j < numItems - i; j++) to for (int j = 0; j < numItems - i - 1; j++)

Because if i is 0, there will be j < numItems, and sorted[j] = sorted[j+1] will be out of range.