为什么只返回“是”？ [英] Why is this only returning "yes"

问题描述

int OnLoad() {
cout << "Hi whats your name? ";
cin >> name;
system("cls");
cout << "Hi " << name << "." << " Are you here to Take Over the city from zombies?"<< endl;
cin >> userInput;
if (userInput == "yes" || "Yes") {
    cout << "Yes" << endl;
}
else if (userInput == "no" || "No") {
    cout << "No" << endl;
}
else {
    cout << "I don't understand." << endl;
}
return 0;
}

int main() {
OnLoad();
system("pause");
return 0;
}

此代码仅在控制台窗口弹出并询问是您即使在我键入no之后也可以从僵尸手中接管城市。

This code only returns Yes back, after the console window pops up and ask are you here to take over the city from zombies even after i type no it returns yes!

推荐答案

if (userInput == "yes" || "Yes")

实际上是

if ((userInput == "yes") || ("Yes"))

这是两个表达式之间的逻辑或： userInput ==是 和是 。第一个是正确的，直接评估为 bool 。第二个只是 char * ，它将隐式转换为 bool 。由于它是一个编译时间字符串，因此不能为 nullptr ，这意味着它将始终评估为 true 。反过来，这意味着整个条件始终为 true （这就是逻辑OR的工作方式）。
正确的代码是

It's logical OR between two expressions: userInput == "yes" and "Yes". The first one is correct and evaluates to bool directly. The second one is just a char* that will be converted to bool implicitly. Since it's a compile time string it cannot be nullptr, which means it will always evaluate to true. And that, in turn, means the whole condition is always true (that's how logical OR works). The correct code is

if (userInput == "yes" || userInput == "Yes")

P。 S.这就是为什么我总是建议尽可能使用最高警告级别进行编译（对于MSVC， / W4 ， -Wall -pedantic-errors 用于GCC和clang）。在这种情况下，大多数编译器都会生成警告。

P. S. This is why I always recommend compiling with the highest warning level possible (/W4 for MSVC, -Wall -pedantic-errors for GCC and clang). Most compilers will generate a warning in this case.

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