Insertion Sort in C

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

void output(int *array,int size)
{
  int i;

  for (i = 0; i < size; i++) 
  {
    printf("%d\n", array[i]);
  }
}
void insertion_sort(int *array,int size)
{
  int i,j,key;

  for (i = 1; i < size; i++) 
  {
    key = array[i];
    j = i - 1;
    while((j >= 0) && (array[j] > key))
    {
      array[j + 1] = array[j];
      j--;
    }
    array[j + 1] = key;
  }
}

int main()
{
  int *a = malloc(sizeof(int));
  int i = 0;

  while(scanf("%d", &a[i]))
  {
    if (a[i] == -1){break;}
    i++;
    a = realloc(a, i*sizeof(int));
  }

  insertion_sort(a,i);

  output(a,i);

  return 0;
}