[C] Pascals Triangle Generation

Code:

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

#define SWAP(x, y) (               \
                     ((x) ^= (y)), \
                     ((y) ^= (x)), \
                     ((x) ^= (y))  \
                   )

size_t nCr(size_t n, size_t r)
{
  size_t m = n - r;
  if (m > r) { SWAP(m, r); }
  size_t f[] = {1, 1};
  size_t i = r + 1;
  for (; i <= n; ++i) f[0] *= i;
  for (i = 2; i <= m; ++i) f[1] *= i;
  return f[0] / f[1];
}

size_t **PascalsTriangle(size_t num_rows)
{
  size_t **triangle = malloc(sizeof(size_t) * num_rows);
  size_t b = 1;
  for (size_t i = 0; i < num_rows; ++i) {
    triangle[i] = malloc(sizeof(size_t) * b);
    triangle[i][0] = triangle[i][b - 1] = 1;
    for (size_t j = 1; j < b - j; ++j) {
      triangle[i][j] = triangle[i][b - j - 1] = nCr(i, j);
    }
    ++b;
  }
  return triangle;
}

int main()
{
  const int num_rows = 10;
  size_t **pascals_triangle = PascalsTriangle(num_rows);
  for (int i = 0; i < num_rows; ++i) {
    for (int j = 0; j < i + 1; ++j) {
      printf("%d ", pascals_triangle[i][j]);
    }
    free(pascals_triangle[i]);
    printf("\n");
  }
  free(pascals_triangle);
}

Code:

1 
1 1 
1 2 1 
1 3 3 1 
1 4 6 4 1 
1 5 10 10 5 1 
1 6 15 20 15 6 1 
1 7 21 35 35 21 7 1 
1 8 28 56 70 56 28 8 1 
1 9 36 84 126 126 84 36 9 1