2.6 布尔值

原文来自：http://www.learncpp.com/cpp-tutorial/26-boolean-values/

布尔值只有两个可能的值：true(1)和false(0).

用bool进行声明：

   1: bool bValue;

 

有两种方式进行赋值：

   1: bool bValue1 = true; // explicit assignment

   2: bool bValue2(false); // implicit assignment

 

正如操作符-能够使得一个正数变成一个负数，逻辑操作符！能够将布尔型值取相反的一个。

   1:  

   2:  bValue1 = !true; // bValue1 will have the value false

   3:  bValue2(!false); // bValue2 will have the value true

 

布尔型变量并不被解释为true或false，而是0或1.因此，当输出一个布尔型变量时，false的值输出0，true的值输出1.

 

   1: bool bValue = true;

   2: cout << bValue << endl;

   3: cout << !bValue << endl;

   4:  

   5: bool bValue2 = false;

   6: cout << bValue2 << endl;

   7: cout << !bValue2 << endl;

 

输出：

1

0

0

1

布尔变量最常用在if语句中。

   1: bool bValue = true;

   2: if (bValue)

   3:     cout << "bValue was true" << endl;

   4: else

   5:     cout << "bValue was false" << endl;

输出

bValue was true

同样：

   1: bool bValue = true;

   2: if (!bValue)

   3:     cout << "The if statement was true" << endl;

   4: else

   5:     cout << "The if statement was false" << endl;

结果：

The if statement was false

用布尔型变量来作为函数的返回值也是很有用的，能够检测一些东西是否正确。如：

   1: #include <iostream>

   2:  

   3: using namespace std;

   4:  

   5: // returns true if x and y are equal

   6: bool IsEqual(int x, int y)

   7: {

   8:     return (x == y); // use equality operator to test if equal

   9: }

  10:  

  11: int main()

  12: {

  13:     cout << "Enter a value: ";

  14:     int x;

  15:     cin >> x;

  16:  

  17:     cout << "Enter another value: ";

  18:     int y;

  19:     cin >> y;

  20:  

  21:     bool bEqual = IsEqual(x, y);

  22:     if (bEqual)

  23:         cout << x << " and " << y << " are equal"<<endl;

  24:     else

  25:         cout << x << " and " << y << " are not equal"<<endl;

  26:     return 0;

  27: }

 

 

我们也可以直接在if语句判断体中调用函数。

   1: if (IsEqual(x, y))

   2:     cout << x << " and " << y << " are equal"<<endl;

   3: else

   4:     cout << x << " and " << y << " are not equal"<<endl;

当将整型变量转变成布尔型时，0被解释为false，非零值被解释为true。