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The typeof keyword returns an instance of the System.Type class when passed a name of a class. It is similar to the sizeof keyword in that it returns a value instead of starting a section (block) of code (see if, try, while).

An example:

using System;

namespace MyNamespace
{
    class MyClass
    {
        static void Main(string[] args)
        {
            Type t = typeof(int);
            Console.Out.WriteLine(t.ToString());
            Console.In.Read();
        }
    }
}

The output will be:

System.Int32

It should be noted that unlike sizeof, only class names themselves and not variables can be passed to typeof as shown here:

using System;

namespace MyNamespace
{
    class MyClass2
    {
        static void Main(string[] args)
        {
            char ch;
            
            // This line will cause compilation to fail
            Type t = typeof(ch);
            Console.Out.WriteLine(t.ToString());
            Console.In.Read();
        }
    }
}

Sometimes, classes will include their own GetType() method that will be similar, if not identical, to typeof.



C# Keywords
abstract as base bool break
byte case catch char checked
class const continue decimal default
delegate do double else enum
event explicit extern false finally
fixed float for foreach goto
if implicit in int interface
internal is lock long namespace
new null object operator out
override params private protected public
readonly ref return sbyte sealed
short sizeof stackalloc static string
struct switch this throw true
try typeof uint ulong unchecked
unsafe ushort using var virtual
void volatile while
Special C# Identifiers (Contextual Keywords)
add alias async await dynamic
get global nameof partial remove
set value when where yield
Contextual Keywords (Used in Queries)
ascending by descending equals from
group in into join let
on orderby select where