example.c

   1 #!/usr/bin/env cscript
   2
   3 /* SPDX-License-Identifier: GPL-2.0
   4  *
   5  * Copyright (C) 2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
   6  */
   7
   8 #define _GNU_SOURCE
   9
  10 #include <stdint.h>
  11 #include <stddef.h>
  12 #include <stdlib.h>
  13 #include <stdio.h>
  14 #include <inttypes.h>
  15 #include <errno.h>
  16
  17 enum { PASCALS_TRIANGLE_MAX_ROWS_FOR_UINT64 = 68 };
  18
  19 static uint64_t **create_pascals_triangle(size_t num_rows)
  20 {
  21         uint64_t **triangle;
  22         size_t i, j;
  23
  24         if (!num_rows || num_rows > PASCALS_TRIANGLE_MAX_ROWS_FOR_UINT64) {
  25                 errno = EINVAL;
  26                 return NULL;
  27         }
  28
  29         triangle = reallocarray(NULL, num_rows + 1, sizeof(*triangle));
  30         if (!triangle)
  31                 return NULL;
  32         triangle[num_rows] = NULL;
  33
  34         for (i = 0; i < num_rows; ++i) {
  35                 triangle[i] = reallocarray(NULL, i + 1, sizeof(**triangle));
  36                 if (!triangle[i]) {
  37                         for (j = 0; j < i; ++j)
  38                                 free(triangle[j]);
  39                         free(triangle);
  40                         return NULL;
  41                 }
  42                 triangle[i][0] = triangle[i][i] = 1;
  43                 for (j = 1; j < i; ++j)
  44                         triangle[i][j] = triangle[i - 1][j - 1] + triangle[i - 1][j];
  45         }
  46
  47         return triangle;
  48 }
  49
  50 static void free_pascals_triangle(uint64_t **triangle)
  51 {
  52         size_t i;
  53
  54         if (!triangle)
  55                 return;
  56
  57         for (i = 0; triangle[i]; ++i)
  58                 free(triangle[i]);
  59         free(triangle);
  60 }
  61
  62 static void print_pascals_triangle(FILE *file, uint64_t **triangle)
  63 {
  64         size_t i, j;
  65
  66         for (i = 0; triangle[i]; ++i) {
  67                 for (j = 0; j < i + 1; ++j)
  68                         fprintf(file, "%" PRIu64 " ", triangle[i][j]);
  69                 fputc('\n', file);
  70         }
  71 }
  72
  73 int main(int argc, char *argv[])
  74 {
  75         uint64_t **triangle;
  76         size_t num_rows;
  77         char *endptr;
  78
  79         if (argc != 2) {
  80                 fprintf(stderr, "Usage: %s ROWS\n", argv[0]);
  81                 return 1;
  82         }
  83
  84         num_rows = strtoul(argv[1], &endptr, 10);
  85         if (!*argv[1] || *endptr) {
  86                 fprintf(stderr, "ERROR: `%s' is not a valid number\n", argv[1]);
  87                 return 1;
  88         }
  89
  90         triangle = create_pascals_triangle(num_rows);
  91         if (!triangle) {
  92                 perror("ERROR: unable to create triangle");
  93                 return 1;
  94         }
  95         print_pascals_triangle(stdout, triangle);
  96         free_pascals_triangle(triangle);
  97
  98         return 0;
  99 }