决定一个数是完全数还是素数 [英] deciding if a number is perfect or prime

问题描述

问题是:编写一个函数来判断一个数是质数还是完全数."

the problem is : "Write a function to find out if a number is a prime or perfect number."

到目前为止，我已经完成了完美的部分，这就是我所拥有的:

so far i have worked on the perfect part first and this is what i have:

#include <iostream>
using namespace std;
bool perfectNumber(int);
int main()
{
 int number;

 cout<<"Please enter number:\n";
 cin>>number;
 bool perfectNumber(number);

 return 0;
}
bool perfectNumber(int number)
{
 int i;

 int sum=0;
 for(i=1;i<=number/2;i++)
 {
  if(number%i==0)
  {
   sum+=i;
  }
 }
 if (sum==number)
  return i;
 else
  return 0;
}

然而，这段代码似乎有错误.我看过这本书，但没有谈到这个话题.我想获得有关如何修复此代码的建议.

HOWEVER, there seems to be errors on this code. I have looked over the book but nothing talks about this topic. i would like to get advice on how to fix this code.

谢谢！

推荐答案

bool perfectNumber(number);

这不会调用perfectNumber函数；它声明了一个名为 perfectNumber 的 bool 类型的局部变量，并用转换为 bool 类型的 number 的值来初始化它.

This does not call the perfectNumber function; it declares a local variable named perfectNumber of type bool and initializes it with the value of number converted to type bool.

为了调用 perfectNumber 函数，您需要使用以下内容:

In order to call the perfectNumber function, you need to use something along the lines of:

bool result = perfectNumber(number);

或:

bool result(perfectNumber(number));

另外一点:如果您要从流中读取输入(例如 cin>>number)，您必须检查以确保从流中提取值成功.现在，如果您输入 asdf，提取将失败并且 number 将保持未初始化状态.检查提取是否成功的最好方法是简单地测试流的状态:

On another note: if you are going to read input from a stream (e.g. cin>>number), you must check to be sure that the extraction of the value from the stream succeeded. As it is now, if you typed in asdf, the extraction would fail and number would be left uninitialized. The best way to check whether an extraction succeeds is simply to test the state of the stream:

if (cin >> number) {
    bool result = perfectNumber(number);
}
else {
    // input operation failed; handle the error as appropriate
}

您可以在 Semantics ofbasic_ios 上的标志.您还应该查阅一本优秀的入门级 C++ 书籍以了解更多信息流式使用最佳做法.

You can learn more about how the stream error states are set and reset in Semantics of flags on basic_ios. You should also consult a good, introductory-level C++ book for more stream-use best practices.

这篇关于决定一个数是完全数还是素数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！