如何在N下找到第一个素数 [英] How do I find the first primes under N

问题描述

我写了一个代码来列出变量N下的素数，我不明白为什么它不会工作。这是我的代码：

i have written a code to list the primes under a variable N, i dont understand why it wont work. here is my code:

int N, i, j;
boolean isPrime;
Scanner scanner = new Scanner(System.in);
System.out.println("Enter value of N:");
N = scanner.nextInt();

for (j=2; j <=N; j++) {

    isPrime = true;

    for (i=2; i<=j ; i++) {

        if (j%i == 0) {

            isPrime = false;
            System.out.println(+j);
            break;

        }
    }

    if(isPrime == true){
    System.out.println(+j);

    }

我的尝试：



我在休息之前输入了一个打印声明，它只打印了我不理解的每个数字

What I have tried:

I have put in a print statement before the break and it just prints every number which i dont understand

推荐答案

问题是 i 循环在最后一次迭代时将数字除以。

尝试

The problem is that the i loop divide the number by itself on last iteration.
Try

for (i=2; i<j ; i++) {

有一个工具可以让你看到你的代码在做什么，它的名字是调试器。它也是一个很好的学习工具，因为它向你展示了现实，你可以看到哪种期望与现实相符。

当你不明白你的代码在做什么或为什么它做它做的时候，答案就是答案是调试器。

使用调试器查看代码正在执行的操作。只需设置断点并查看代码执行情况，调试器允许您逐行执行第1行并在执行时检查变量。



调试器 - 维基百科，免费的百科全书 [ ^ ]

http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html [ ^ ]

https://www.jetbrains.com/idea/help/debugging-your-first-java-application.html [ ^ ]

调试器在这里向您展示你的代码正在做，你的任务是与它应该做的事情进行比较。

调试器中没有魔法，它没有找到错误，它只是帮助你。当代码没有达到预期的效果时，你就会接近一个错误。

There is a tool that allow you to see what your code is doing, its name is debugger. It is also a great learning tool because it show you reality and you can see which expectation match reality.
When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]
http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html[^]
https://www.jetbrains.com/idea/help/debugging-your-first-java-application.html[^]
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

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