在c ++中验证double [英] Validating a double in c++

问题描述

我完全不熟悉编码，因此在注释之前请记住这一点。

I'm completely new to coding, so please keep this in mind before commenting.

所以我一直试图进入编码一段时间，今天我去图书馆
并拿起一本书叫c ++编程。我写了一些基本的程序，
，但我陷入了一点，我不知道如何创建一个函数
确保当用户提示双，他们进入已验证。
（如果用户输入k这样的字符，程序就会中断）。
我在这里和网上搜索，并有一些答案，但他们更多沿着
这里的一行代码工作，插入x，y，z到它的行。而我不
有足够的经验知道该怎么办。所以这里是一个混合代码
从另一个问题，我没有尝试使其工作在我的程序：

So I've been trying to get into coding for a while, and today I went to the library and picked up a book called "programming in c++". I've written some basic programs, but I have gotten stuck at one point, I have no idea how to create a function that makes sure that when the user is prompted for a double, what they enter is valid. (If the user enters a character like 'k', the program just breaks). I searched here and on the net, and there are some answers, but they are more along the line of "here's a line of code that works, insert x, y, z, into it". And I don't have enough experience to know what to do. So here is a sample that is a mix of code from another question, and me failing to try to make it work in my program:

#include <iostream>
#include <stdio.h>


using namespace std;

double GetDouble () {
    double x;
    cin >> x;
    int valid = 0;
    while (valid == 0) {
        if (x == double) {
      return x;
      break;
  } else if (x != double) {
      cout << "Invalid Input! Please input a numerical value." << endl;
      cin.clear();
      while (cin.get() != '\n') ; // empty loop
    }
}
return x;
}

现在我想要做的是使用cin< x来获得用户对x的输入，然后
然后确保x是双精度，我在这里失败了。如果
有人可以解释这一点，以澄清每个操作，
我会真正感谢。例如，我不知道break函数的作用，
和cin.clear（）和cin.get（）做什么。 （我知道这是一个重复，但在另一个问题的
答案根本不说明我很困惑，
谢谢你花时间阅读& answer this！：

Now what I want it to do is to use "cin << x" to get a user input for x, and then make sure that x is a double, and I'm failing quite hard at this. If someone could explain this to in a manner that clarifies each operation, I would be truly grateful. For example, I don't know what the break function does, and what the cin.clear(), and cin.get() do. (I know this is a duplicate, but the answers on the other question does not at all address what I'm confused about, thank you for taking time to read & answer this! :)

推荐答案

这似乎是你的代码的一个接近的模拟（大部分）：

This seems a close analog to your code that (mostly) works:

double GetDouble () {
    double x;
    cin >> x;
    // ver1: while( cin.fail() ) // or !cin.good()   no trailing char check.
    while( cin.fail() || (cin.peek() != '\r' && cin.peek() != '\n'))
    {
        cout << "Invalid Input! Please input a numerical value." << endl;
        cin.clear();
        while( cin.get() != '\n' ); // or cin.ignore(1000, '\n');
        cin >> x;
    }
    return x;
}

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