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.
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
*/
The default value of a bool variable is false. The default value of a bool? variable is null.
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#:
int x = 123;
// if (x) // Error: "Cannot implicitly convert type 'int' to 'bool'"
{
Console.Write("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:
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 it is a letter, it checks if it is lowercase or uppercase. These checks are performed with the IsLetter, and IsLower, both of which return the bool type:
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 language specification is the definitive source for C# syntax and usage.
See Also
Reference
Integral Types Table (C# Reference)
Built-In Types Table (C# Reference)
Implicit Numeric Conversions Table (C# Reference)
Explicit Numeric Conversions Table (C# Reference)