Bubble sort of structures using pointers in C

Question

I want to sort an array of structures using the bubble sort algorithm and pointers in C. I have a cars structure:

typedef struct{
    char model[30];
    int hp;
    int price;
}cars;

and I allocate memory for 12 items:

cars *pointer = (cars*)malloc(12*sizeof(cars));

and read data from file:

for (i = 0; i <number ; i++) {
    fscanf(file, "%s %i %i\n", (pointer+i)->model, &(pointer+i)->hp, &(pointer+i)->price);
}

I pass pointer ptr to bubbleSort function:

bubbleSort(pointer, number);

Here is my bubbleSort function:

void bubbleSort(cars *x, int size) {
    int i, j;
    for (i=0;i<size-1;i++) {
    int swapped = 0;
    for (j = 0; j < size - 1 - i; j++) {
        if ( (x+i)->hp > (x+j+1)->hp ) {
            cars *temp = (x+j+1);
            x[j+1] = x[j];
            x[j] = *temp;
            swapped = 1;
        }
    }
        if (!swapped) {
        //return;
        }
    }
}

The problem is that I don't know how to swap items using pointers.

Answer 1

Consider the following solution for sorting function:

void bubbleSort(cars *x, int size) 
{
    int i, j;
    for (i = 0; i < size-1; i++) 
    {
        for (j = 0; j < size-1-i; j++) 
        {
            if ( x[j].hp > x[j+1].hp ) 
            {
               cars temp = x[j+1];
               x[j+1] = x[j];
               x[j] = temp;
            }
        }
    }
}

The problem was in the data swap part

Answer 2

void bubbleSort(cars *x, int size)
{
        int i, j;
        cars temp;

        for (i=0;i<size-1;i++) {
            for (j = i+1; j < size; j++) {
                if ( (x+i)->hp > (x+j)->hp ) {
                    temp = x[j];
                    x[j] = x[i];
                    x[i] = temp;
                }
            }
        }
}

This is a reply to a comment under this code; it demonstrates that the sort that I suggest swaps less ... :) Here the code:

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

typedef struct {
    int x;
    int hp;
} cars;

int swaps;

void bubbleSortB(cars *x, int size)
{
        int i, j;
        cars temp;

        for (i=0;i<size-1;i++) {
            for (j = i+1; j < size; j++) {
                if ( (x+i)->hp > (x+j)->hp ) {
                    temp = x[j];
                    x[j] = x[i];
                    x[i] = temp;
                    swaps++;
                }
            }
        }
}

void bubbleSortA(cars *x, int size)
{
    int i, j;
    for (i = 0; i < size-1; i++)
    {
        for (j = 0; j < size-1-i; j++)
        {
            if ( x[j].hp > x[j+1].hp )
            {
               cars temp = x[j+1];
               x[j+1] = x[j];
               x[j] = temp;
               swaps++;
            }
        }
    }
}

int main(void)
{
    int i;

    cars x[10]={ {1,4},{1,8},{1,12},{1,6},{1,5},{1,4},{1,8},{1,12},{1,6},{1,5} };
    cars y[10]={ {1,4},{1,8},{1,12},{1,6},{1,5},{1,4},{1,8},{1,12},{1,6},{1,5} };

    swaps=0;
    bubbleSortA(x,10);
    for(i=0;i<10;i++)
        printf("%d ",x[i].hp);
    printf("- swaps %d\n",swaps);

    swaps=0;
    bubbleSortB(y,10);  //My sort
    for(i=0;i<10;i++)
        printf("%d ",y[i].hp);
    printf("- swaps %d\n",swaps);

}

Answer 3

Use a swap function like this:

#define TYPE <your type>
void swap(TYPE *a, TYPE *b){
        TYPE *temp = (TYPE*)malloc(sizeof(TYPE));
        *temp = *a;
        *a = *b;
        *b = *temp;
        free(temp);
}

Or this one, without malloc:

void swap(TYPE *a, TYPE *b){
        TYPE temp;
        temp = *a;
        *a = *b;
        *b = temp;
}