你可以解释如何布尔可以控制回路？

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问题描述

我在C ++（目前）初学者程序员，我有一个概念上的问题。

I'm a beginner programmer in C++ (currently), and I've got a conceptual question.

我试图过滤一霉素输入，以确保它是01-04之间的一或二位的整数，并且如果它不是，以产生一个错误，并要求一个新的输入。

I'm trying to filter a cin input to ensure that it is a one-or-two-digit integer between 01-04, and if it isn't, to produce an error and ask for a new input.

我还使用地图来给用户一个选项列表，在有效的选择，线路输入（整数），通过任何几种方法制作一个相关的结果，但我会问其他地方这个问题的一个更具体的版本。

I'm also using map to give the user a list of options that, upon valid selection, routes inputs (integers) through any of several methods to produce a relevant result, but I'll ask a more specific version of this question elsewhere.

我发现code的片段在，是为了验证输入。我有点明白了，除非布尔条件设置while循环中。因为我不明白，这使得它很难编辑或确保我操纵它的权利。

I found a snippet of code at http://www.cplusplus.com/forum/beginner/26821/ that is meant to validate an input. I sort of get it, except where the boolean condition is set inside the while loop. Because I don't understand it, it makes it very difficult to edit or make sure that I'm manipulating it right.

下面是例子code：

int main()
{
    int num;
    bool valid = false;

    while (!valid)
    {
        valid = true; //Assume the cin will be an integer.

        cout << "Enter an integer value: " << endl;
        cin >> num;

        if(cin.fail()) //cin.fail() checks to see if the value in the cin
                    //stream is the correct type, if not it returns true,
                    //false otherwise.
        {
            cin.clear(); //This corrects the stream.
            cin.ignore(); //This skips the left over stream data.
            cout << "Please enter an Integer only." << endl;
            valid = false; //The cin was not an integer so try again.
        }
    }

    cout << "You entered: " << num << endl;

    system("PAUSE");
    return 0;

这是我的code（整个事情，给上下文）。我不认为这是完整的，我只是想确保我使用布尔权利。

And here is my code (the entire thing, to give context). I don't think it's complete, I just want to make sure I'm using the boolean right.

float _tmain(float argc, _TCHAR* argv[])
{
    bool validInput = !true;

    map<string,int> Operations;
    Operations.insert(pair<string, int>("Addition", 01));
    Operations.insert(pair<string, int>("Subtraction", 02));
    Operations.insert(pair<string, int>("Multiplication", 03));
    Operations.insert(pair<string, int>("Division", 04));

    cout << "Welcome to OneOpCalc, what operation would you like to perform?" << endl;

    for(map<string, int>::iterator ii=Operations.begin(); ii!=Operations.end(); ++ii)
    {
        cout << (*ii).second << ": " << (*ii).first << endl;
    }

    while (!validInput)
    {
        cin >> operatorSelection;

        if (cin.fail() || operatorSelection < 4 || operatorSelection > 1)
        {
            cout << "Error: Invalid selection. Please choose a valid number." << endl << endl;
            cin.clear();
            cin.ignore();
        }
    }
}

确实而（！有效）的意思是当有效是假的？在我的头，它说虽然有效是！有效，这很明显，将永远是假的。

Does while (!valid) mean "While valid is false"? In my head, it's saying "While valid is !valid", which obviously, would always be false.

编辑：感谢球员，我期待通过他们所有的答案。一个答案我一直得到那张过于笼统;我明白那个！是不是，我理解翻转使用它的布尔的概念。然而，隐含的逻辑含义是什么让我困惑。在任何给定的声明，我习惯了的思维有效作为翻转有效价值的一种方式！;未测试的条件。它是用它来测试一个条件，即招数我的语法。换句话说，写而（！有效）字面上读我为而（NOTvalid），而不是而（有效== FALSE）。我不能让自己明白，为什么在这种情况下，！有效读为条件，而不是只是有点翻转。

Thanks for the answers guys, I'm looking through them all. One answer I keep getting goes too general; I understand that ! is NOT, and I understand the concept of flipping the bool using it. However the implicit logical implications are what confuse me. In any given statement, I am used to thinking of !valid as a way of flipping the valid value; Not testing a condition. It's the syntax of using it to test a condition that tricks me. In other words, writing while(!valid) reads literally to me as while(NOTvalid), not while(valid==false). I can't get myself to understand why in this case, !valid reads as a condition and not just a bit-flip.

Valid

你可以解释如何布尔可以控制回路？

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