Bool

Bool is often used in expressions. Many C# expressions evaluate to a boolean value. Represented in 1 byte, the bool type represents truth.

We often use a bool in the condition of a while-loop. An infinite loop can be expressed as a while-true loop. Booleans make useful flag variables.

First program

A bool can be assigned to the true and false literals. We set the bool variable to true. And then we invert the value of the bool using the exclamation operator.

using System;

bool val = true;
if (val)
{
    Console.WriteLine(val == true);
}
val = !val;
if (!val)
{
    Console.WriteLine(val == false);
}
True
True

Bool variable

This program declares a bool variable. It manipulates its values through expressions. The size of the bool type is one byte. It is aliased to the System.Boolean type.

using System;

// Part 1: set values to bool.
bool value = true;
Console.WriteLine(value);

value = !value;
Console.WriteLine(value);

value = false;
Console.WriteLine(value);

// Part 2: use if-statements with bool.
if (value)
{
    Console.WriteLine("Not reached");
}
if (!value)
{
    Console.WriteLine("Reached");
}

// Part 3: use a bool local to store an expression result.
bool test = !value && 1 == int.Parse("1");
Console.WriteLine(test);

// Part 4: print bool details.
Console.WriteLine(sizeof(bool));
Console.WriteLine(true.GetType());
True
False
False
Reached
True
1
System.Boolean

Ints, bools

How can you convert an int in your C# program to a bool value? This can be done with the Convert.ToBoolean method in the System namespace. A custom method could also be used.

using System;

Console.WriteLine(Convert.ToBoolean(5));
Console.WriteLine(Convert.ToBoolean(0));
Console.WriteLine(Convert.ToBoolean(-1));
True
False
True

Null bool

A bool cannot be null—its default value is false. But we can use a nullable bool, which is a struct that wraps a bool value, and set it to null.

using System;

// A null bool can mean an uninitialized boolean value.
bool? valid = null;
Console.WriteLine("Initialized: {0}", valid.HasValue);

// We can then set the nullable bool to true or false.
valid = true;
Console.WriteLine("Valid: {0}", valid.Value);
Initialized: False
Valid: True

Bools can be used in a variety of places to represent truth values. They are used throughout programs—even if you do not notice them.

Nearly every C# program uses bools. All if-statements requires a boolean expression. We explored bools, established their representation size in bytes, and tested conversions.