Java程序给出两个区间之间的素数

Question

我需要一个程序来打印任意两个间隔之间的所有素数，然后打印两个间隔之间有多少个素数。

所以我有一个正在运行的代码，但它不会打印数字 2，而且我知道 2 是素数。它正在正确地执行其他所有操作。我尝试了一些其他可以打印 2 的代码，但如果我输入负数，它也会给出负数。

import java.util.Scanner;

class Main {

  public static void main(String args[]) {

    int first, last, flag = 0, i, j;

    Scanner scanner = new Scanner(System.in);

    System.out.print("\nEnter the lower bound : ");
    first = scanner.nextInt();
    System.out.print("\nEnter the upper bound : ");
    last = scanner.nextInt();
    System.out.println("The prime numbers in between the entered limits are :");

    int x = 0;
    for (i = first; i <= last; i++) {
      for (j = 2; j < i; j++) {
        if (i % j == 0) {
          flag = 0;
          break;
        } else {
          flag = 1;
        }
      }
      if (flag == 1) {
        x++;
        System.out.println(i + " ");
      }
    }
    System.out.println("Total number of prime numbers between " + first + " and " + last + " are " + x);
  }
}

所以如果我输入 -5(上限)和 10(下限)它应该打印:2357-5 到 10 之间的质数总数为 4

但是它打印357-5 到 10 之间的质数总数为 3

Answer 1

只需在 for 循环之前添加以下几行，它就会给出预期的输出:

int x = 0;
if (first<3) {
    System.out.println(2);
    x++;
}

您的更新程序将是:

import java.util.Scanner;

class Main {

  public static void main(String args[]) {

    int first, last, flag = 0, i, j;

    Scanner scanner = new Scanner(System.in);

    System.out.print("\nEnter the lower bound : ");
    first = scanner.nextInt();
    System.out.print("\nEnter the upper bound : ");
    last = scanner.nextInt();
    System.out.println("The prime numbers in between the entered limits are :");

    int x = 0;
    if (first<3) {
        System.out.println(2);
        x++;
    }
    for (i = first; i <= last; i++) {
      for (j = 2; j < i; j++) {
        if (i % j == 0) {
          flag = 0;
          break;
        } else {
          flag = 1;
        }
      }
      if (flag == 1) {
        x++;
        System.out.println(i + " ");
      }
    }
    System.out.println("Total number of prime numbers between " + first + " and " + last + " are " + x);
  }
}