bool (C# Reference)
The bool keyword is an alias of System.Boolean. It is used to declare variables to store the Boolean values, true and false.
Note
If you require a Boolean variable that can also have a value of null, use bool?. For more information, see Nullable Types (C# Programming Guide).
Literals
You can assign a Boolean value to a bool variable. You can also assign an expression that evaluates to bool to a bool variable.
// keyword_bool.cs
using System;
public class MyClass
{
static void Main()
{
bool i = true;
char c = '0';
Console.WriteLine(i);
i = false;
Console.WriteLine(i);
bool Alphabetic = (c > 64 && c < 123);
Console.WriteLine(Alphabetic);
}
}
Output
True False False
Conversions
In C++, a value of type bool can be converted to a value of type int; in other words, false is equivalent to zero and true is equivalent to nonzero values. In C#, there is no conversion between the bool type and other types. For example, the following if statement is invalid in C#, while it is legal in C++:
int x = 123;
if (x) // Invalid in C#
{
printf("The value of x is nonzero.");
}
To test a variable of the type int, you have to explicitly compare it to a value, such as zero, as follows:
int x = 123;
if (x != 0) // The C# way
{
Console.Write("The value of x is nonzero.");
}
Example
In this example, you enter a character from the keyboard and the program checks if the input character is a letter. If so, it checks if it is lowercase or uppercase. These checks are performed with the IsLetter, and IsLower, both of which return the bool type:
// keyword_bool_2.cs
using System;
public class BoolTest
{
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.");
}
}
}
Input
X
Sample Output
Enter a character: X The character is uppercase. Additional sample runs might look as follow: 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 on bool and related subjects, see the following sections in the C# Language Specification:
4.1.8 The bool Type
7.9.4 Boolean Equality Operators
7.11.1 Boolean Conditional Logical Operators
See Also
Reference
C# Keywords
Integral Types Table (C# Reference)
Built-In Types Table (C# Reference)
Implicit Numeric Conversions Table (C# Reference)
Explicit Numeric Conversions Table (C# Reference)