Const keyword

• Const variable in C# are compile time variable i.e value is known at compile time.
• The assignment to const variable is only done at the time of declaration and this value of variable remain constant throughout lifetime of the program.
• These variable are accessed via "Classname.Variablename".
• Such variable can be declared and intialized in any method of class.

Readonly keyword

• Readonly is a keyword which when used with a variable then the value of that variable can only be changed either at runtime or at the time of the instance initialization.
• The assignment to readonly variable is only done at the time of declaration or through constructor of the class.
• These variable are accessed via "Instancename.Variablename".
• Readonly keyword cannot be used with variables in the methods even the value of readonly variable cannot be changed in any method of the class.