Bubble sort isn't working while sorting in ascending order

Question

I have created a program that seeks input from the users about a 5 digit number (char datatype used) and it bubble sorts it out based upon the ascending or descending order, depending upon the parameter set in if statement.

CASE 1 : if (a[j] < a[j+1])

• Input : 12345
• Desired output : 54321
• Output : 12345 - Works

CASE 2 : if (a[j] > a[j+1])

• Input : 54321
• Desired output : 12345
• Does not work.

Here's my code below :

int main()
{
    char a[6];
    int i, temp;
    int j = 0;

    printf("Enter a 5 digit number\n");
    scanf("%s", a);

    printf("You entered : %s\n", a);

    for ( i = 0 ; i < 5 ; i++ )
    {
        for ( j = 0 ; j < 6 - 1 - i ; ++j )
        {
            if ( a[j] > a[j+1] )
            {
                temp = a[j];
                a[j] = a[j+1];
                a[j+1] = temp;
            }
        }
    }
    
    printf("Bubble Sorted number : %s\n", a);

    return 0;
}

Answer 1

This inner for loop

    for ( j = 0 ; j < 6 - 1 - i ; ++j )
    {
        if ( a[j] > a[j+1] )
        {
            temp = a[j];
            a[j] = a[j+1];
            a[j+1] = temp;
        }
    }

can overwrite the terminating zero character '\0' of the string stored in the array a.

When in the outer loop the variable i is equal to 0 then you have actually the following inner loop

    for ( j = 0 ; j < 5 ; ++j )
    {
        if ( a[j] > a[j+1] )
        {
            temp = a[j];
            a[j] = a[j+1];
            a[j+1] = temp;
        }
    }

In this case when j in the loop will be equal to 4 then the expression a[j+1] that is the same as a[5] will yield the terminating zero character that will be swapped with the character stored in the array element a[4].

Rewrite the inner loop like

    for ( j = 1 ; j < 6 - 1 - i ; ++j )
    {
        if ( a[j-1] > a[j] )
        {
            temp = a[j-1];
            a[j-1] = a[j];
            a[j] = temp;
        }
    }