C Bubble Sort Biggest Value Turns into 0

Question

I am a not a professional so please, bear with me.

I am in the process of learning C, and for practice I made a small program that reads a couple of numbers from argv, and sorts them in ascending order.

So far it works pretty well. Except for 2 things:

1. The program adds an extra zero to the list (I know why this is happening, but don't feel like fixing it right now)
2. The biggest number somehow turns into a zero in the process (I don't know why this is happening and I want to fix it)

I am specifically concerned with Issue #2.

For example, when running ./a.out 6 8 4 9 3 the output comes out to 0 0 3 4 6 8 instead of 0 3 4 6 8 9 (once again I'm only concerned with the disappearance of the 9)

I am using gcc version 7.3.1 on Linux if it helps.

Why does the biggest number turn into a zero?

The code:

#include <stdio.h>
#include <stdlib.h>

void flip(short position, short * values){
    int key = values[position];
    values[position] = values[position + 1];
    values[position + 1] = key;
}


void sort(short * values, short argc){
    for( short iterations = argc; iterations > 0; --iterations){
            for( short position = 1; position < iterations; ++position){
                    if (values[position] > values[position + 1])
                            flip(position, values);
            }
    }

    for ( short i = 0; i < argc; ++i )
            printf("%d ", values[i]);
    printf("\n");
}

int main(short argc, char **argv){
    if ( argc <= 1 ){
            fprintf( stderr, "USAGE: %s <<short int>...>\n", argv[0] );
            return 1;
    }

    short *values = malloc(sizeof(short) * (argc-1));

    for (int i = 1; i < argc; ++i ){ 
            values[i] = strtol(argv[i], NULL, 0);
    }

    sort(values, argc);

    return 0;
}

Any help would very much be appreciated.

Edit: Having had run it through GDB I figured out that the issue is in not in the main function, as x/6uh values still returns the correct values when sort starts. The issue occurs while I am inside flip. Still not sure what the problem is though...

Answer 1

Your main problem is that you need to store the values in the array starting at values[0], and you mistakenly call your sort routine with argc which is too big. Try something like this:

#include <stdio.h>
#include <stdlib.h>

void flip(int position, int * values){
    int key = values[position];
    values[position] = values[position + 1];
    values[position + 1] = key;
}


void sort(int * values, int numvals){
    for( int iterations = numvals - 1; iterations >= 0; --iterations){ //TODO
            for( int position = 0; position < iterations; ++position){
                    if (values[position] > values[position + 1])
                            flip(position, values);
            }
    }

    for ( int i = 0; i < numvals; ++i )
            printf("%d ", values[i]);
    printf("\n");
}

int main(int argc, char **argv){
    if ( argc <= 1 ){
            puts("Did not specify any arguments. Exiting...");
            return 1;
    }

    int *values = malloc(sizeof(int) * (argc-1));

    for (int i = 1; i < argc; ++i ){
            values[i-1] = strtol(argv[i], NULL, 0);
    }

    sort(values, argc - 1);

    return 0;
}

I changed your shorts to ints, but that likely doesn't matter except for argc.