Question

从我从书中读到的内容以及我从书中所做的先前例子来看，这就是我所提出的。我很欣赏额外的建议，但我正在努力学习本章试图向我展示的内容，以便在我尝试以前从未见过的代码之前，我可以继续学习基础知识。我希望用户输入0来结束循环但由于某种原因循环继续？我想我可能会遗漏一些阻止它停止的东西。

// Ex4_08.cpp
// Initializing pointers with strings
#include <iostream>
using std::cin;
using std::cout;
using std::endl;

int main()
{
    bool keepgoing = true;
    int answer;
    while (keepgoing = true)
    {

        const char* pstr[]{ "Aa",                                       // Initializing a pointer array
            "Bb",
            "Cc",
            "Dd",
            "Ee",
            "Ff",
            "Gg",
            "Hh",
            "Ii",
            "Jj",
            "Kk",
            "Ll",
            "Mm",
            "Oo",
            "Pp",
            "Qq",
            "Rr",
            "Ss",
            "Tt",
            "Uu",
            "Vv",
            "Ww",
            "Ss",
            "Yy",
            "Zz",

        };
        const char* pstart{ "Your letter is " };

        int dice{};

        cout << endl
            << "Enter a number between 1 and 26 " << _countof(pstr) << ": ";
        cin >> dice;

        cout << endl;
        if (dice >= 1 && dice <= _countof(pstr))                            // Check input validity
            cout << pstart << pstr[dice - 1];                               // Output star name

        else
            cout << "Sorry, you haven't selected a correct number.";        // Invalid input


        cout << "Do you want to do this again? Type 0 for no: " << endl;
        cin >> answer;
        if (answer == 0)
        {
            keepgoing = false;
        }

    }


    cout << endl;
    return 0;
}

Answer 1

我使用了更多C ++且更易于使用的vector和string修改了初始代码示例：

#include <iostream>
#include <string> // for string
#include <vector>  // for vector
using std::cin;
using std::cout;
using std::endl;

int main()
{
    std::vector<std::string> pstr;

    for (char c = 'a'; c <= 'z'; c++)  // cycle over the 26 ASCII letters
    {
        std::string temp;     // 
        temp += c - 32;       //  add capital character (e.g A)
        temp += c;            //  add character (e.g. a)
        pstr.push_back(temp); // push the new string (e.g. Aa) to the vector 
    }

    const char* pstart{ "Your letter is " };

    int dice{};

    while (true)
    {
        cout << endl
            << "Enter a number between 1 and 26 " << pstr.size() << ": ";
        cin >> dice;
        if (dice == 0)
        {
            break; //break if the user enters 0
        }
        cout << endl;
        if (dice >= 1 && dice <= pstr.size())                            // Check input validity
            cout << pstart << pstr[dice - 1];                               // Output star name

        else
            cout << "Sorry, you haven't selected a correct number.";                    // Invalid input
    }
    cout << endl;
    return 0;
}

Answer 2

你的代码错了：

while (keepgoing = true) {
  ...
  if (answer == 0) {
    keepgoing = false;
  }
}

您将keepgoing设置为false，但在while条件下，您将其置于true。您必须使用==运算符（如while(keepgoing == true)中所述）或将其删除（while(keepgoing)）。

否则，您可以使用while(true)或for (;;)而不是keepgoing = false：

for (;;) { // or while (true); to me, that's only a matter of preference.
  ...
  if (answer == 0) {
    break; // exit the loop
  }
}

在您输入break条件之前，它们会产生无限循环。

Answer 3

更改此行：

while (keepgoing = true)

对此：

while (keepgoing == true)

第一个将值true指定给变量keepgoing。对keepgoing的值的第二次检查是true。这是一个非常普遍的问题，许多新程序员（有时是旧程序员）的绊倒。： - ）

扩展我的阵列

3 个答案: