java - While 循环 1 - 100 之间的素数

Question

我对编程还很陌生，我正在努力理解循环。我设法让一段代码正常工作，但我仍然没有完全理解它是如何工作的。我在网上找到了一个类似程序的代码，该程序是使用 for 循环编写的，并且我设法让它作为 while 循环工作(花了我几天的时间!!!)。我试图了解内部循环在做什么。

我知道外循环正在检查循环的每次迭代的x是否小于100。为什么需要在循环中嵌套y变量，为什么将其设置为2以及为什么每次都需要加1？另外，有没有办法在不使用 break; 的情况下退出循环？

我在这里看到了此类程序的一些其他示例，但我希望有人能够阐明这个程序的具体工作原理。

提前致谢!!!

class PrimeNumbers {
  public static void main(String args[]) {
    int x = 2;
    while (x <= 100) {
      int y = 2;
      while (y <= x) {
        if (x == y) {
          System.out.println(x);
        }
        if (x % y == 0) {
          break;
        }
        y++;
      }
      x++;
    }
  }
}

Answer 1

评论是你的 friend :

class PrimeNumbers {
    public static void main(String args[]) {
        // No point checking below 2 since the definition of a prime is "A prime number (or a prime) is a natural number greater than 1 ..."
        int x = 2;
        // Looking for primes up-to and including 100
        while (x <= 100) {
            // Same argument as above - start checking at 2 and work upwards.
            int y = 2;
            // stop when y > x as obviously y will not divide x
            while (y <= x) {
                // if y reaches x then we have not found any divisors
                if (x == y) {
                    // success! This x is prime.
                    System.out.println(x);
                }
                // if y divides x leaving no remainder then not prime - give up this y loop and select our next x
                if (x % y == 0) {
                    break;
                }
                // Try next y divisor.
                y++;
            }
            // Try next x candidate.
            x++;
        }
    }
}

并为变量命名更有帮助，它会变得更加容易

class PrimeNumbers {
    public static void main(String args[]) {
        // No point checking below 2 since the definition of a prime is "A prime number (or a prime) is a natural number greater than 1 ..."
        int candidate = 2;
        // Looking for primes up-to and including 100
        while (candidate <= 100) {
            // Same argument as above - start checking at 2 and work upwards.
            int divisor = 2;
            // stop when divisor > candidate as obviously divisor will not divide candidate
            while (divisor <= candidate) {
                // if divisor reaches candidate then we have not found any divisors (because of the `break` below).
                if (candidate == divisor) {
                    // success! This candidate is prime.
                    System.out.println(candidate);
                }
                // if divisor divides candidate leaving no remainder then not prime - give up this divisor loop and select our next candidate
                if (candidate % divisor == 0) {
                    break;
                }
                // Try next divisor.
                divisor++;
            }
            // Try next candidate.
            candidate++;
        }
    }
}