Sorting array of numbers in C

Question

// code to sort array of 16 numbers, but output isnt quite correct.
// must use pointers to array addresses
// final output is -451 993 384 201 89 77 38 28 16 12 7 1 0 -2 -5 -17
// as you can see -451 isn't in the right place.

output

-451 7 993 1 0 16 -5 12 89 28 77 384 -2 38 -17 201

-451 -17 993 7 1 16 0 12 89 28 77 384 -2 38 -5 201

-451 993 -17 7 1 16 0 12 89 28 77 384 -2 38 -5 201

-451 993 7 -17 1 16 0 12 89 28 77 384 -2 38 -5 201

-451 993 7 1 -17 16 0 12 89 28 77 384 -2 38 -5 201

-451 993 16 7 1 -17 0 12 89 28 77 384 -2 38 -5 201

-451 993 16 7 1 0 -17 12 89 28 77 384 -2 38 -5 201

-451 993 16 12 7 1 0 -17 89 28 77 384 -2 38 -5 201

-451 993 89 16 12 7 1 0 -17 28 77 384 -2 38 -5 201

-451 993 89 28 16 12 7 1 0 -17 77 384 -2 38 -5 201

-451 993 89 77 28 16 12 7 1 0 -17 384 -2 38 -5 201

-451 993 384 89 77 28 16 12 7 1 0 -17 -2 38 -5 201

-451 993 384 89 77 28 16 12 7 1 0 -2 -17 38 -5 201

-451 993 384 89 77 38 28 16 12 7 1 0 -2 -17 -5 201

-451 993 384 89 77 38 28 16 12 7 1 0 -2 -5 -17 201

-451 993 384 201 89 77 38 28 16 12 7 1 0 -2 -5 -17

total exchanges: 68

#include <stdio.h>

#define N 16

int xchg();

int main() {
    int numbers[16] = {7, 1, 993, -5, 0, 16, -451, 12, 89, 28, 77, 384, -2, 38, -17, 201}; 
    int cntr, cntr2, cntr3;
    int chgNum;

    for(cntr = 0; cntr < N; cntr++){
        for(cntr2 = 1; cntr2 < N; cntr2++){
            chgNum += xchg(&numbers[cntr], &numbers[cntr2]);
        }
        for(cntr3 = 0; cntr3 < N; cntr3++){
            if(cntr3 == 15){
                printf("%d", numbers[cntr3]);
            }
            else {
                printf("%d ", numbers[cntr3]);
            } 
        }

        printf("\n");


    }
    printf("total exchanges: %d\n", chgNum);
    return 0;
}

int xchg(int *p1, int *p2) {
    int tmp = 0;
    if(*p2 < *p1){
        tmp = *p1;
        *p1 = *p2;
        *p2 = tmp;
        return 1;
    }
    else {
        return 0;
    }
}

Answer 1

You need to change your loop in main .

for(cntr2 = cntr+1; cntr2 < N; cntr2++){

You might also want to check if xchg is giving you the direction ascending/descending sort order or if you need to invert your exchange condition.

Also: you forgot to initialize chgNum to zero.

Answer 2

Ok the problem is that the inner for loop starts at 1, after the first iteration it will be wrong it needs to start at the position that the first loop is at, ie cntr2 = cntr.

A few other things:

• The forward declaration of the `xchng` function isn't correct.
• The if else print statement doesn't do anything it will print the same thing no matter what.
• If you are incrementing a number using `++` operator and it isn't being assigned to anything, always use `++(int)`, it requires fewer operations.
• Finally, there are some nasty variable names, it doesn't hurt to be more descriptive. Also you define a macro which is the size of the array, but you don't define the array using it, int numbers[N] would make more sense as then at least you can see why the the macro is used in the loop.