C++中的运算符总结（4）：逻辑运算符（下）

以下程序演示了如何使用条件语句和逻辑运算符根据变量的值执行不同的代码行：

#include <iostream>
using namespace std;int main()
{cout << "Use boolean values(0 / 1) to answer the questions" << endl;cout << "Is it raining? ";bool isRaining = false;cin >> isRaining;cout << "Do you have buses on the streets? ";bool busesPly = false;cin >> busesPly;// Conditional statement uses logical AND and NOTif (isRaining && !busesPly)cout << "You cannot go to work" << endl;elsecout << "You can go to work" << endl;if (isRaining && busesPly)cout << "Take an umbrella" << endl;if ((!isRaining) && busesPly)cout << "Enjoy the sun and have a nice day" << endl;return 0;
}

输出：

Use boolean values(0 / 1) to answer the questions
Is it raining? 1
Do you have buses on the streets? 1
You can go to work
Take an umbrella

再次运行的输出：

Use boolean values(0 / 1) to answer the questions
Is it raining? 1
Do you have buses on the streets? 0
You cannot go to work

最后一次运行的输出：

Use boolean values(0 / 1) to answer the questions
Is it raining? 0
Do you have buses on the streets? 1
You can go to work
Enjoy the sun and have a nice day

第 15 行包含条件表达式 (isRaining && !busesPly)，可将其读作 “下雨且没有公交车”。这个表达式使用了逻辑 AND 运算符将没有公交车（对有公交车执行逻辑 NOT 运算）和下雨关联起来。

以下程序演示了如何将逻辑运算符 NOT 和 OR（ ! 和 ||）用于条件处理。

#include <iostream>
using namespace std;int main()
{cout << "Answer questions with 0 or 1" << endl;cout << "Is there a discount on your favorite car? ";bool onDiscount = false;cin >> onDiscount;cout << "Did you get a fantastic bonus? ";bool fantasticBonus = false;cin >> fantasticBonus;if (onDiscount || fantasticBonus)cout << "Congratulations, you can buy that car!" << endl;elsecout << "Sorry, waiting a while is a good idea" << endl;if (!onDiscount)cout << "Car not on discount" << endl;return 0;
}

输出：

Answer questions with 0 or 1
Is there a discount on your favorite car? 0
Did you get a fantastic bonus? 1
Congratulations, you can buy that car!
Car not on discount

再次运行的输出：

Answer questions with 0 or 1
Is there a discount on your favorite car? 0
Did you get a fantastic bonus? 0
Sorry, waiting a while is a good idea
Car not on discount

最后一次运行的输出：

Answer questions with 0 or 1
Is there a discount on your favorite car? 1
Did you get a fantastic bonus? 1
Congratulations, you can buy that car!  

分析：

这个程序建议您能够打折或得到很高的补贴时就把车买了，不然就再观望观望。它还在第 19 行使用了逻辑非运算来提醒您不打折。第 14 行使用了一条 if 语句，而第 16 行是与之配套的 else 语句。在条件 (onDiscount || fantasticBonus) 为 true 时，将执行第 15 行的语句。这个表达式包含逻辑运算符||，仅当您喜欢的汽车打折或能够获得很高的补贴时， 该表达式才为 true。当该表达式为 false 时， 将执行 else语句后面的语句（第 17 行）。

该文章会更新，欢迎大家批评指正。

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