c++ - 如何找出为什么我的程序一直有无限循环？

Question

我似乎找不到我的代码有什么问题，我试图在答案等于 0 时结束循环，但它一直在无限循环中。

#include <iostream>
int main() {
    using namespace std;
    int x, remainder;
    cout << "please enter a positive integer number: " << endl;
    string tab;
    tab = '\t';
    cin >> x;
    remainder = x % 2;

    do{
        while ( x % 2 != 0)
        {
            cout << x << " is odd" << tab << "Subtract 1" << tab << " Half of " << x - 1 << " is " << x / 2;
            x = (x - 1) / 2;
            cout  << endl;

        }

        while (x % 2 == 0)
        {
            cout << x << " is even" << tab << "Subtract 0" << tab << "Half of  " << x << " is " << x / 2;
            x = x / 2;
            cout << endl;
        }

    }
    while (x >= 0);  
}

Answer 1

本质上，您的代码中存在两个问题，这两个问题本身都会使您的循环无休止地运行。

从外部开始并向内工作:(外部)while 循环结束时的测试将始终为“true”，因为您有 while (x >= 0) ;因此，即使 x 变为零(它会如此)，循环仍将继续运行! (而且，一旦 x 为零，它将保持为零!)

其次，两个“内部”while 循环根本不应该是循环!您希望一个或另一个“ block ”在每个主循环中只运行一次 - 所以使用 if ... else 结构。

以下是您的代码的更正版本:

#include <iostream>

int main() {
//  using namespace std; // Generally, not good practice (and frowned-upon here on SO)
    using std::cin;  using std::cout; using std::endl; // Use only those you want to!
    using std::string;
    int x, remainder;
    cout << "please enter a positive integer number: " << endl;
    string tab;
    tab = '\t';
    cin >> x;
    remainder = x % 2;

    do {
        if (x % 2 != 0)
        {
            cout << x << " is odd" << tab << "Subtract 1" << tab << " Half of " << x - 1 << " is " << x / 2;
            x = (x - 1) / 2;
            cout << endl;
        }
        else // if (x % 2 == 0) ... but we don't need to test this again.
        {
            cout << x << " is even" << tab << "Subtract 0" << tab << "Half of  " << x << " is " << x / 2;
            x = x / 2;
            cout << endl;
        }
    } while (x > 0); // You run forever if you have x >= 0!
    return 0;
}

还有一些其他的东西可以更改以使代码更“高效”，但在我们开始编辑 BPC(最佳可能代码)之前，我会让您仔细阅读 MNC(最小必要更改) )!

编辑:好的，由于来自评论的“同行压力”😊，我现在将放入一个建议 BPC:

#include <iostream>

int main() {
    using std::cin;  using std::cout; using std::endl; // Use only those you want to!
    int x;// , remainder; // "remainder" is never used, so we can discard it!
    cout << "Please enter a positive integer number: " << endl;
    cin >> x; // Not critical, but I like to put such a cin right after the prompting cout.
    std::string tab{ "\t" }; // Let's initialise more directly!
    do {
        // As there is only one line (now) inside each if/else block, we can leave out the {} ...
        if (x % 2 != 0)
            cout << x << " is odd" << tab << "Subtract 1" << tab << "Half of " << x - 1 << " is " << x / 2;
        else
            cout << x << " is even" << tab << "Subtract 0" << tab << "Half of  " << x << " is " << x / 2;
        // We can put the following two line outside the tests, as they will be the same in both cases:
        x = x / 2; // When x is ODD, this will give the SAME answer as x = (x - 1)/2 (as you noticed in your first cout)
        cout << endl;
    } while (x > 0); // You run forever if you have x >= 0!
    return 0;
}