Question

我正在尝试制作一个小型操作系统，它可以从一个开关......案例中获得一个微型游戏或一个简单的计算器。但是，无论我给出什么输入（甚至是正确的输入），输出始终是默认值。我正在使用的编译器（Microsoft Visual Studio;它可能是问题）并没有给我任何错误，我无法找到或想到任何错误。你们中有些真正擅长的人对我的问题有任何答案吗？

#include "stdafx.h"
#include <iostream>
#include <limits>

using namespace std;

int calc() {

char op;
float num1, num2;

cout << "Enter operation:";
cin >> op;

cout << "Enter two numbers:";
cin >> num1 >> num2;

switch (op)
{
case '+':
    cout << num1 + num2;
    break;

case '-':
    cout << num1 - num2;
    break;

case '*':
    cout << num1 * num2;
    break;

case '/':
    cout << num1 / num2;
    break;

default:
    cout << "That is not an operation";
    break;
}

return 0;
};

int main()
{
char answer;

cout << "Welcome to the FR Operating System. \n";
cout << "If you want to go to the calculator, type in 'Calc'. \n";
cout << "If you want to go to the game, type in 'Game'. \n";

cin >> answer;

switch (answer) {
case 'Calc' || 'calc':
    cout << "Welcome to the calculator. \n";
    break;

case 'Game':
    cout << "Welcome to our game, 'A Day in the Life'. \n";
    break;

default:
    cout << "That is an invalid answer. This has caused the system to crash. \n";
    break;
}

atexit([] { system("PAUSE"); });

return 0;

}

Answer 1

'Game'不是有效的字符串
即使您将"Game"替换为有效字符串，switch也无法使用字符串。

因此，要么在您的交换机中使用单个字符，要么使用if - else个阻止您通过std::string比较==。

std::string answer;
cin >> answer;
if (answer == "Calc" || answer == "calc")
    //...
else if (answer == "Game")
    //...
else
    // invalid

Answer 2

使用map to item回调

理想情况下，将项目菜单映射到其各自的操作会更好。 std::map<std::string, std::function<void()>>允许这一点！阅读内联评论以了解其余部分：

#include <string>
#include <map>
#include <iostream>
#include <functional>

int main()
{
    std::map<std::string, std::function<void()>> menu_items;
    menu_items.emplace("calc", [](){std::cout << "calculate chosen\n";}); //use lambdas to spare boilerplate
    menu_items.emplace("game", [](){std::cout << "game is chosen\n";});

    std::string chosen_item;
    std::cin >> chosen_item;
    auto item = menu_items.find(chosen_item); //search by the string
    if (item == menu_items.end()) //item was not found in the list
        std::cout << "invalid item is chosen\n";
    else
        item->second(); //execute the stored function
}

Demo

根据您的使用情况，您可能希望将void*()用于std::function<void()>，将std::unordered_map用于std::map。对于您的使用案例，它似乎并不重要。

此外，您可能希望规范化输入，例如小写字符串，或执行一些其他规范化。由于这不是代码中对性能敏感的部分，因此我认为std::function和std::map的开销在这种情况下无关紧要。

Answer 3

当变量iFileNum = FreeFile Open strNotesPath For Input As iFileNum While Not EOF(iFileNum) Line Input #iFileNum, strText If Left(strText, 3) = "===" Then strText = "" If lngIndex + 1 <= ActivePresentation.Slides.Count Then lngIndex = lngIndex+1 Set NotesPLC = getPLC(ActivePresentation.Slides(lngIndex)) If Not b_append Then NotesPLC.TextFrame.DeleteText Else If Not NotesPLC Is Nothing Then NotesPLC.TextFrame.TextRange = _ NotesPLC.TextFrame.TextRange & vbCrLf & strText End If为string时，您正在提示用户answer，将提示更改为char和c等字符，从而使其成为g更方便，因此您可以在switch / case声明中使用和枚举字符：

int main()
{
char answer;

cout << "Welcome to the FR Operating System. \n";
cout << "If you want to go to the calculator, type in 'c'. \n";
cout << "If you want to go to the game, type in 'g'. \n";
cin >> answer;
switch (answer) {
case 'c':
case 'C':
    cout << "Welcome to the calculator. \n";
    break;

case 'g':
case 'G':
    cout << "Welcome to our game, 'A Day in the Life'. \n";
    break;
...

Switch Case始终为默认值

3 个答案:

使用map to item回调