Question

I am participating in Harvard’s opencourse ware and attempting the homework questions. I wrote (or tried to) write a program in C to sort an array using bubble sort implementation. After I finished it, I tested it with an array of size 5, then 6 then 3 etc. All worked. then, I tried to test it with an array of size 11, and then that’s when it started bugging out. The program was written to stop getting numbers for the array after it hits the array size entered by the user. But, when I tested it with array size 11 it would continuously try to get more values from the user, past the size declared. It did that to me consistently for a couple days, then the third day I tried to initialize the array size variable to 0, then all of a sudden it would continue to have the same issues with an array size of 4 or more. I un-did the initialization and it continues to do the same thing for an array size of over 4. I cant figure out why the program would work for some array sizes and not others. I used main to get the array size and values from the keyboard, then I passed it to a function I wrote called sort. Note that this is not homework or anything I need to get credit, It is solely for learning. Any comments will be very much appreciated. Thanks.

/**************************************************************************** 
 * helpers.c
 *
 * Computer Science 50
 * Problem Set 3
 *
 * Helper functions for Problem Set 3.
 ***************************************************************************/

#include <cs50.h>
#include <stdio.h>

#include "helpers.h"

void 
sort(int values[], int n);

int main(){

    printf("Please enter the size of the array \n");
    int num = GetInt();
    int mystack[num];
    for (int z=0; z < num; z++){
        mystack[z] = GetInt();
    }

    sort(mystack, num);
}


/*
 * Sorts array of n values.
 */

void 
sort(int values[], int n)
{
    // this is a bubble sort implementation
    bool swapped = false; // initialize variable to check if swap was made

    for (int i=0; i < (n-1);){ // loops through all array values

        if (values[i + 1] > values [i]){ // checks the neighbor to see if it's bigger
            i++; // if bigger do nothing except to move to the next value in the array
        }
        else{ // if neighbor is not bigger then out of order and needs sorting
            int temp = values[i]; // store current array value in temp variable for swapping purposes
            values[i] = values[i+1]; //swap with neighbor
            values[i+1] = temp; // swap neighbor to current array value
            swapped = true; // keep track that swap was made
            i++;
       }

       // if we are at the end of array and swap was made then go back to beginning
       // and start process again.
       if((i == (n-1) && (swapped == true))){ 
           i = 0;
           swapped = false;
       }

       // if we are at the end and swap was not made then array must be in order so print it
       if((i == (n-1) && (swapped == false))){
           for (int y =0; y < n; y++){
                printf("%d", values[y]);
           }
           // exit program
           break; 
       }

   } // end for

   // return;
}

Answer 1

As it turns out the reason why it was doing this is because when comparing an array’s neighbor to itself as in:

if (values[i + 1] > values [i])

The fact that I was just checking that it is greater than, without checking if it is ‘=’ then it was causing it to behave undesirably. So if the array is for example [1, 1, 5, 2, 6, 8] then by 1 being next to a 1, my program did not account for this behavior and acted the way it did.