Question

This is a weird error that I am getting for a simple selection sort.

Use the following inputs 89,52,10,1,56,63,24,36,12,5

If you were to debug it you would notice that during the 3rd iteration the line
a[i]=a[i] ^ a[min]; sets both operand to zero.

Any Idea why this is happening ?

#include<stdio.h>

int main()
{
    int a[10]={'\0'};
    int i=0,j=0,k=0;
    int min=0;

    printf("Enter 10 Elements\n");

    for(i=0;i<10;i++)
    {
        scanf("%d",&a[i]);
    }

    for(i=0;i<10;i++)
    {
        min=i;

        for(j=i+1;j<10;j++)
        {
            if(a[j]<a[min])
            {
                min=j;
            }
        }


        a[i]=a[i] ^ a[min];
        a[min]= a[min] ^ a[i];
        a[i]= a[i] ^ a[min];
    }

    for(i=0;i<10;i++)
    {
        printf("\n %d",a[i]);
    }

    return(0);
}

Answer 1

XOR is a lousy way to swap variables. Just declare a temporary and use assignments.

The XOR trick:

x = x ^ y;
y = y ^ x;
x = x ^ y;

fails if x and y are the same location in memory; it will then set the value to 0.

I haven’t analyzed your code in detail, but I’ll bet that this:

a[i]=a[i] ^ a[min];
a[min]= a[min] ^ a[i];
a[i]= a[i] ^ a[min];

is failing when i == min.

…

Confirmed, I tried running the program with an added printf statement, and with the specified input it does the swap with i == min at least once.