a routine I am working on to process sets of numbers

makepairs.c

#include <stdlib.h>
#include <stdio.h>
#include "numbers.h" // https://gist.github.com/911872

struct Pair
{
    int left;
    int right;
};
struct Pairs
{
    struct Pair *pairs;
    int size;
};

/*  makePairs
    input:      struct numbers
    output:     struct Pairs

    Inputs a numbers structure {size, values} and constructs all possible
    pairs of the numbers.
    
    For any sequence of unique numbers of size N, there are Sum([N, N-1, N-2, ...) - N.size possible unique pairs.
    This does not take into account permutations on the pairs

    So for example, given a list of numbers [1, 2, 3, 4]
    There are 1 + 2 + 3 + 4 - 4 = 6 total pairs
    [1, 2] [1, 3] [1, 4]
    [2, 3] [2, 4]
    [3, 4]

    There would be twice as many pairs if you consider swapped order, which I should
    like to do later when I construct combined pairs after filtering these pairs.
*/

struct Pairs makePairs(struct numbers myList)
{
    int i, j, k = 0;
    struct Pairs myPairs;
    myPairs.size = sumRange(&myList)-myList.size;
    myPairs.pairs = malloc((sizeof(struct Pair)) * myPairs.size-myList.size);
    for (i = 0; i < myList.size; i++)
    {
        for (j = i+1; j < myList.size; j++)
        {
            myPairs.pairs[k].left = myList.values[i];
            myPairs.pairs[k].right = myList.values[j];
            k++;
        }
    }
    return myPairs;
}
void printPairs(struct Pairs *myPairs)
{
    int i;
    for (i = 0; i < myPairs->size; i++)
    {
        printf("[%03d, %03d] ",myPairs->pairs[i].left, myPairs->pairs[i].right);
    }
    printf("\n");
}