Docs-.NET-C # - Guide - Language Reference - keyword - value types: bool

ylbtech-Docs-.NET-C # - Guide - Language Reference - keyword - value types: bool

 

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bool (C # Reference)

• 2015/07/20

bool Keywords are  System.Boolean  alias. It is used to declare variables to store Boolean values: to true  and  false .

 Remark

To support the three-valued logic (for example, when using three-valued Boolean database support), use  bool? type. For  bool? operands predefined  & and  | operator supports three-valued logic. For more information, see the Boolean operator a text may be a Boolean operator is null section.

text

Boolean values can be assigned to  bool variables. The results can also be as a  bool type of expression assigned to  bool a variable.

C#copy

public class BoolTest
{
    static void Main()
    {
        bool b = true;

        // WriteLine automatically converts the value of b to text.
        Console.WriteLine(b);

        int days = DateTime.Now.DayOfYear;


        // Assign the result of a boolean expression to b.
        b = (days % 2 == 0);

        // Branch depending on whether b is true or false.
        if (b)
        {
            Console.WriteLine("days is an even number");
        }
        else
        {
            Console.WriteLine("days is an odd number");
        }   
    }
}
/* Output:
  True
  days is an <even/odd> number
*/

bool The default value of variables  false. bool? The default value of variables null .

Change

In C ++, bool the value type can be converted to  int value type; that is, false equivalent to a zero value, and  true is equivalent to a non-zero value. In C #, there is no  bool conversion between types of other types. For example, the following  if statement is invalid in C #:

C#copy

int x = 123;

// if (x)   // Error: "Cannot implicitly convert type 'int' to 'bool'"
{
    Console.Write("The value of x is nonzero.");
}

To test  int the type of a variable, the variable must be a value (e.g., zero) an explicit comparison, as follows:

C#copy

if (x != 0)   // The C# way
{
    Console.Write("The value of x is nonzero.");
}

Examples

In this example, you enter a character from the keyboard, and then enter the program checks whether a character is a letter. If the character is a letter, then it checks its case. These checks are performed using  IsLetter  and  islower , both return  bool types:

C#copy

public class BoolKeyTest
{
    static void Main()
    {
        Console.Write("Enter a character: ");
        char c = (char)Console.Read();
        if (Char.IsLetter(c))
        {
            if (Char.IsLower(c))
            {
                Console.WriteLine("The character is lowercase.");
            }
            else
            {
                Console.WriteLine("The character is uppercase.");
            }
        }
        else
        {
            Console.WriteLine("Not an alphabetic character.");
        }
    }
}
/* Sample Output:
    Enter a character: X
    The character is uppercase.
 
    Enter a character: x
    The character is lowercase.

    Enter a character: 2
    The character is not an alphabetic character.
 */

 

C # Language Specification

For more information, see the  C # language specification . The specification language is C # syntax and usage of authoritative information.

See

• C # Reference
• C # Programming Guide
• C # keywords
• Integer type
• Built-in type table

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https://docs.microsoft.com/zh-cn/dotnet/csharp/language-reference/keywords/bool

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Author: ylbtech Source: http://ylbtech.cnblogs.com/ This article belongs to the author and blog Park total, welcome to reprint, but without the author's consent declared by this section must be retained, and given the original connection in the apparent position of the article page, otherwise reserves the right to pursue legal responsibilities.