不熟悉这个, 给你一个链接

给你找到这个

www.programmingsimplified.com/c/source-code/c-program-for-prime-number

Prime number program in c: c program for prime number, this code prints prime numbers using c programming language. To check whether a number is prime or not see another code below. Prime number logic: a number is prime if it is divisible only by one and itself. Remember two is the only even and also the smallest prime number. First few prime numbers are 2, 3, 5, 7, 11, 13, 17....etc. Prime numbers have many applications in computer science and mathematics. A number greater than one can be factorized into prime numbers, For example 540 = 2²*3³*5¹

Prime number program in c language

#include<stdio.h>
 
int main()
{
   int n, i = 3, count, c;
 
   printf("Enter the number of prime numbers required\n");
   scanf("%d",&n);
 
   if ( n >= 1 )
   {
      printf("First %d prime numbers are :\n",n);
      printf("2\n");
   }
 
   for ( count = 2 ; count <= n ;  )
   {
      for ( c = 2 ; c <= i - 1 ; c++ )
      {
         if ( i%c == 0 )
            break;
      }
      if ( c == i )
      {
         printf("%d\n",i);
         count++;
      }
      i++;
   }
 
   return 0;
}

Download Prime number program.

Output of program:

C program for prime number or not

#include<stdio.h>
 
main()
{
   int n, c = 2;
 
   printf("Enter a number to check if it is prime\n");
   scanf("%d",&n);
 
   for ( c = 2 ; c <= n - 1 ; c++ )
   {
      if ( n%c == 0 )
      {
         printf("%d is not prime.\n", n);
	 break;
      }
   }
   if ( c == n )
      printf("%d is prime.\n", n);
 
   return 0;
}

C program for prime number using function

#include<stdio.h>
 
int check_prime(int);
 
main()
{
   int n, result;
 
   printf("Enter an integer to check whether it is prime or not.\n");
   scanf("%d",&n);
 
   result = check_prime(n);
 
   if ( result == 1 )
      printf("%d is prime.\n", n);
   else
      printf("%d is not prime.\n", n);
 
   return 0;
}
 
int check_prime(int a)
{
   int c;
 
   for ( c = 2 ; c <= a - 1 ; c++ )
   { 
      if ( a%c == 0 )
	 return 0;
   }
   if ( c == a )
      return 1;
}

There are many logic to check prime numbers, one given below is more efficient then above method.
for ( c = 2 ; c <= (int)sqrt(n) ; c++ )
Only checking from 2 to square root of number is sufficient.
There are many more efficient logic available.

所有跟帖： 

• 谢谢！我是一窍不通的，等他回来我给他看你的建议。 -So_Be_It- ♀ (0 bytes) () 12/04/2014 postreply 08:22:06

• 我找到一个网上的例子了。别看我的了。修改了内容。 -秋月冬雪- ♀ (33 bytes) () 12/04/2014 postreply 08:23:42

• 從數學來說好像可以優化一點 -violinpiano- ♂ (132 bytes) () 12/04/2014 postreply 08:30:31

• 是的，这样优化得多。 -秋月冬雪- ♀ (6 bytes) () 12/04/2014 postreply 08:31:21

• 算法可以优化： -heure- ♂ (304 bytes) () 12/04/2014 postreply 08:31:33