如何在用户给出n的位置打印所有素数no.s [英] How do I print all the prime no.s upto n where n is given by user

问题描述

public class test
{
public static void main(String ars[])
{
	Scanner s=new Scanner(System.in);
	System.out.println("enter your range from 1\n");
	int l=s.nextInt();
	while(l!=0)
	{
		for(int i=3;i<=l;i++)
		{	if(i%2==0) 
			{
			break;
			}
			else if((i+2)%i!=0)
				System.out.println(i);		
		}
		l--;
	}
}
}

我尝试了什么：



这里我正在尝试打印素数。从3.因为3％2不是0所以它将来到其他部分，其中5％3！= 0这是真的所以它将打印3现在'i'将增加为4.Since 4％2 == 0所以再次'我'将增加为5.现在它来到其他部分7％5！= 0所以它将打印5.但它没有发生。而不是在第二次迭代得到5我每次都得到3。

What I have tried:

here i'm trying to print the prime no. from 3. since 3%2 is not 0 so it will come to else part where 5%3!=0 which is true so it will print 3 and now 'i' will be incremented as 4.Since 4%2==0 so again 'i' will increment as 5.Now it come to else part where 7%5!=0 so it will print 5. But it's not happening.Instead of getting 5 in 2nd iteration i'm getting 3 everytime.

推荐答案

首先，你的算法找到素数是错误的，完全错误。没有更正，重写是有序的。

对算法进行一些研究，以确定数字是否为素数将有所帮助：

素数 - 维基百科 [ ^ ]

注意1不是素数，它是单位。第一个素数是2.

-----

建议：创建一个函数 isprime ，其任务是检查给定的数字是否是素数。

这样，你就可以分开关注，测试也更容易。

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你的代码没有表现出你期望的方式，或者你不明白为什么！



有一个几乎通用的解决方案：一步一步地在调试器上运行你的代码，检查变量。 br />
调试器在这里向您展示您的代码正在做什么，您的任务是与它应该做什么进行比较。

调试器中没有魔法，它不是'知道你的cpde应该做什么，它没有发现错误，它只是通过向你展示正在发生的事情来帮助你。当代码没有达到预期的效果时，你就接近了一个错误。

要查看你的代码在做什么：只需设置断点并查看代码是否正常运行，调试器允许你执行第1行第1行并在执行时检查变量。



此解决方案的缺点：

- 这是一个DIY，你是跟踪问题并找到根源的那个，这导致了解决方案。

这个解决方案的优点：

- 它也是一个很好的学习工具，因为它告诉你现实，你可以看到哪种期望与现实相符。



次要效果

- 你会为自己找到虫子感到自豪。

- 你的学习技巧会提高。



你应该很快就会发现什么是错的。



调试器 - 维基百科，免费的百科全书 [ ^ ]



掌握Visual Studio 2010中的调试 - 初学者指南 [ ^ ]

使用Visual Studio 2010进行基本调试 - YouTube [ ^ ]

1.11 - 调试你的程序（踩踏和断点）|学习C ++ [ ^ ]

调试器仅显示您的代码正在执行的操作，并且您的任务是与应该执行的操作进行比较。

First of all, your algorithm to find prime number is wrong, plain wrong. There is no correction, a rewrite is in order.
A little study of algorithm to find if a number is prime or not will help:
Prime number - Wikipedia[^]
Note that 1 is not a prime, it is the unit. First prime is 2.
-----
Advice: create a function isprime that will have the task to check if a given number is prime or not.
This way, you separate concerns, and tests are easier.
-----
Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
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 know what your cpde is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
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.

The downside of this solution:
- It is a DIY, you are the one tracking the problem and finding its roots, which lead to the solution.
The upside of this solution:
- It is also a great learning tool because it show you reality and you can see which expectation match reality.

secondary effects
- Your will be proud of finding bugs yourself.
- Your learning skills will improve.

You should find pretty quickly what is wrong.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]
1.11 — Debugging your program (stepping and breakpoints) | Learn C++[^]
The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

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