C 中的质数优化 [英] Prime Numbers Optimization in C

问题描述

我尝试打印质数；2 到 100 万.但是控制台上没有打印任何内容.你能检查我的代码吗?我怎样才能更优化这段代码?

I try to print the prime numbers; 2 to 1 million. But nothing printed on the console. Could you check my code? And how can I be this code more optimized?

这是我的代码:

#include <stdio.h>
#include <math.h>

main()
{
   int num, sr, num2;

   for (num = 2; num <= 1000000; num++) {
      sr = (int) sqrt(num);
      for (num2 = 2; sr % num2 != 0; num2++) {
         if (sr == num2) {
            printf("%d\n", sr);
         }
      }
   }

}

推荐答案

    #include <stdio.h>
    #include <math.h>

    int main(){
    int num, sr, num2;
    int isPrime = 1; // this is a check parameter; isPrime = 0 if number is not prime.
    for(num=2; num<=100; num++){
        sr = (int) sqrt(num);
        for(num2=2; num2 <= sr; num2++){
            //num2 <== sr to stop the innner loop
            if(num%num2 == 0){
                //printf("=========== %d|%d\n", num,num2); // uncomment this to see if a number is divisable
                isPrime = 0; // this number is not prime, cos num can be divided by num2
                break;
            }
        }
        if(isPrime){
            printf("Prime number is %d\n", num);
            isPrime = 1; // reset the check parameter
        }else{
            isPrime = 1; // reset the check parameter
        }
    }
         return 0;
    }

此代码有效.既然它有效，我会让你玩它并优化它.如果你不能让我们知道.我们会尽力帮助您.

This code works. Since it works, i'll let you play with it and optimize it. If you can't let us know. We'll try to help you.

我喜欢你使用 sqrt 优化代码的方式.

I like how you used sqrt to optimize the code.

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