5

Compute prime numbers

  1. #include <math.h>
  2.  
  3. int isprime(int n) {
  4.     double sn;
  5.     int d;
  6.  
  7.     if (n < 2)
  8.         return 0;
  9.     if (n == 2)
  10.         return 1;
  11.     if (n % 2 == 0)
  12.         return 0;
  13.  
  14.     sn = sqrt(n);
  15.  
  16.     for (d = 3; d <= sn; d += 2)
  17.         if (n % d == 0)
  18.             return 0;
  19.     return 1;
  20. }
  21.  
  22. #include <stdio.h>
  23.  
  24. int main() {
  25.     int n;
  26.  
  27.     for (n = 1; n < 100; n++)
  28.         if (isprime(n) )
  29.             printf("%d ", n);
  30.     printf("\n");
  31. }
$ gcc -o prime prime.c -lm
$ ./prime
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 

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