Constant
Const is nothing but “Constant”.
A variable declared as “const” must be assigned a value at declaration, and this value may not then change at a later time.
The Value in a const variable is what is called a “compile-time” value and is immutable.
You can apply const keyword to built-in value type(byte, short, int, long, char, float, double, decimal, bool), enum a string literal, or a reference type which can be assigned with a value null.
Constants can be marked as public, private, protected, internal, or protected internal access modifiers.
Constant the following example :
using System;
namespace ConstandReadonlyExample
{
class ConstantExample
{
const string alpha = "Constant Example";
public ConstantExample()
{
alpha = "Constant Example in c#";
}
void Super()
{
alpha = "Constant";
}
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
}
}
}
ReadOnly
Readonly is the keyword whose value we can change during runtime or we can assign it at run time but only through the non-static constructor. Not even a method.
Readonly the following example :
using System;
namespace ConstandReadonlyExample
{
class ConstantExample
{
readonly String Example;
public Demo()
{
Example = "Readonly Example";
Console.WriteLine(Example);
}
public Demo(string value)
{
Example = value + "Readonly";
Console.WriteLine(Example);
}
}
class Program
{
static void Main(string[] args)
{
Demo d = new Demo();
Demo demo = new Demo("Readonly Example");
Console.ReadKey();
}
}
}
Difference between Readonly and Constant
| Constant | Readonly |
|---|---|
| The Constants are evaluated at compile time. | The Read-Only variables are evaluated at run time. |
| It’s mandatory to assign a value at the time of declaration. eg, int const a=10; |
It’s not mandatory to assign a value at the time of declaration. eg, int read-only a; a=0; |
| Assigned values of constant variables can not be changed. | Read-only variables values can be changed even after assigning. |
| The constant can be declared at the class level as well as inside the method level. | Readonly can be declared only at a class level, not inside the method. |
| Constants in C# provide a named location in memory to store a data value. It means that the value of the variable will be known in compile-time and will be stored in a single place. | The read-only keyword is a modifier that can be used in four contexts: In a field declaration, read-only indicates that assignment to the field can only occur as part of the declaration or in a constructor in the same class. |
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