My quicksort algorithm is giving me a trace trap, how can I fix it?

Question

So currently I am trying to make a quicksort algorithm for an array of strings (to sort them alphabetically) since I can't use the qsort() function for this exercise and I also cannot allocate memory ( malloc() , etc). So, I tried to do it recursively. After testing the first time it worked but as I added more text to the array, it now throws a trace trap which I don't know how to fix.

#include <stdio.h>
#include <string.h>

void swap(char a[], char b[])
{
    char temp[51];
    strcpy(temp, a);
    strcpy(a, b);
    strcpy(b, temp);
}


void quicksort(char array[10000][51], int start, int end)
{

    int i, j, pivot;

    if( start < end )
    {
        pivot = start;
        i = start;
        j = end;

        while( i < j)
        {
            /* i & pivot */
            while( (strcmp(array[i], array[pivot]) <= 0) && i < end )
                i++;

            /* j & pivot */
            while( (strcmp(array[j], array[pivot]) > 0) )
                j--;

            if( i < j )
            {
                swap(array[i], array[j]);
            }
        }

        swap(array[pivot], array[j]);

        quicksort(array, start, j - 1);
        quicksort(array, j + 1, end);

    }
}

The way I call it is pretty simple:

int main()
{
    int i;
    char input[10000][51] = {"this is a test", "another", "fffff", "a" , "skjfkdjf"};

    quicksort(input, 0, 4);

    /* used to print the strings */
    for(i = 0; i < 5; i++)
    {
        printf("%s\n", input[i]);
    }
}

However this throws a trace trap.

If someone could help me find out what is wrong and fix it that would be great!!

Thank you.

Answer 1

The problem is that you're swapping the value with itself here:

swap(array[pivot], array[j]);

I believe:

i = start + 1;

would be a slight optimization, and together with

if (pivot != j) {
    swap(array[pivot], array[j]);       
}

would be sufficient fix.