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  1. // Prime factors.
  2.  
  3. #include <stdlib.h>
  4. #include <stdio.h>
  5.  
  6. #define ARRAY_MAX_SIZE 100
  7. #define ARRAY_INITIALIZER ((struct array) {{}, 0})
  8.  
  9. struct array {
  10.     int p[ARRAY_MAX_SIZE]; size_t n;
  11. };
  12.  
  13. void append(struct array *a, int i)
  14. {
  15.     if (a->n < ARRAY_MAX_SIZE) {
  16.         a->p[a->n++] = i;
  17.     } else {
  18.         fprintf(stderr, "overflow in %s", __func__);
  19.         exit(EXIT_FAILURE);
  20.     }
  21. }
  22.  
  23. void print(const struct array *a, int end)
  24. {
  25.     putchar('[');
  26.     for (size_t i = 0; i < a->n; i++)
  27.         printf("%s%d", i ? ", " : "", a->p[i]);
  28.     putchar(']');
  29.     if (end != 0)
  30.         putchar(end);
  31. }
  32.  
  33. void factor(int n, struct array *r)
  34. {
  35.     for (int i = 2; i*i <= n; i++) {
  36.         while (n%i == 0) {
  37.             append(r, i);
  38.             n = n/i;
  39.         }
  40.     }
  41.     if (n > 1)
  42.         append(r, n);
  43. }
  44.  
  45. int main(void)
  46. {
  47.     struct array r = ARRAY_INITIALIZER;
  48.     factor(2*3*5*7*11*13*17*19*23, &r);
  49.     print(&r, '\n');
  50.     r = ARRAY_INITIALIZER;
  51.     factor(0x80000, &r);
  52.     print(&r, '\n');
  53.     r = ARRAY_INITIALIZER;
  54.     factor(0x7FFFF, &r);
  55.     print(&r, '\n');
  56.     return 0;
  57. }
Success #stdin #stdout 0s 5284KB
comments (?)
stdin 
Standard input is empty
stdout 
[2, 3, 5, 7, 11, 13, 17, 19, 23]
[2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2]
[524287]
https://ideone.com/T3aqDK
language:
C (gcc 8.3)
created:
11 hours ago
visibility:
public

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