Literals and Constants in C Sharp

This post contains information about the C# language literals and constant variables including the readonly modifier.

Literals in C#:

We use literals when we want to provide a variable with a value. Maybe this is upon initialization, or maybe we are fixing the value to be a constant for the run-length of the program. Either way, there are a few rules to adhere to to ensure that the compiler understands what we are asking it for...

Quick Rules:

• Literal values are used for initialization of a variable e.g.:
  
• Most integer literals need no suffix e.g.:
  
• The following integer literals are required to have a suffix:
  
• Floating-point literals should be appended by a suffix:
  
• It is possible to write floating-point literals in 'e' notation:
  
• Boolean valued literals can only be true or false:
  
• Loading hexadecimal numbers into integers:
  
• Literal characters can be typed straight from the keyboard or unicode codes:
  

Constants in C#:

In many applications we require the program to hold numbers that are to be fixed throughout the run-length of the code. There are called constants and there is a special const keyword that we can use to fix the value. By fixing the value we ensure that it cannot be accidentally changed during the run of the code, and provide some data security for compile time. In nerd-speak we call a constant value "immutable".

Once a value (say the value of PI) is labeled const if we try to modify it, either accidentally or on purpose, then the compiler will violently object and we can trace our error.

Quick Rules:

• The const keyword must be used when declaring the variable e.g.:
  
• Constants are implicitly static
  
  
• Both member variables and local variables may be constant
  
  

Examples of const usage:

The readonly modifier in C#:

Variables that have been declared readonly cannot be changed once they have been initialized. This works slightly different to const in that we may declare a readonly variable without an initial value, and then fill it in later.

Quick Rules:

• The readonly keyword must be used when declaring the variable e.g.:
  
• Once readonly values have been initialized they may not be changed
  
  
• Variables declared readonly may be initialized in a constructor, unlike const values which must be fixed at compile time. In fact the primary use of readonly variables is to take on specific values depending upon which class constructor was called.
  
  

Examples of readonly usage:

References:

[1] Wikipedia -- C# Syntax
[2] MSDN -- Value Types
[3] Unicode Lookup Tool
[4] Wikibooks -- C# keyword readonly