-Const
Lets us
look at example
Ex
1
namespace Sample {
public class MyClass
{
private const int a;
}
public class Sample2
{
static void Main()
{
}
}
}
// Outpur Error 1 A const field requires a value to be provided.
Const variable
has to be initialized at the time of declaration and can’t be modified later.
Private static const int a=9; //
Const can’t be marked as static
Ex 2
namespace Sample
{
public class Sample1
{
private const Sample2 sample2 = new Sample2();//Error
}
public class Sample2
{
}
public class Sample3
{
static void Main()
{
}
}
}
//Output Error 1. A const
field of a reference type other than string can only be initialized with null.
A const field of a reference type
other than string can only be initialized with null
Ex 3
namespace Sample
{
public class Sample1
{
private const Sample2 sample2 = null;
}
public class Sample2
{
}
public class Sample3
{
static void Main()
{
}
}
}
// Output No error
Ex4
namespace Sample
{
public class Sample1
{
public const int a = 1;
public const int b = b + 2;
}
public class Sample3
{
static void Main()
{
}
}
}
Value of
b evaluates at compile time, A constant can participate in a constant expression.
-Static
Field
Example
1
namespace Sample
{
public class Sample1
{
public static int c1;
static void Main()
{
Console.WriteLine(c1);
Console.ReadKey();
}
}
}
//Output 0;
Static variable
are initialized as soon as class load with the default value. A
variable in C# can never have an uninitialized value.
-ReadOnly
namespace Sample
{
public class Sample1
{
public static readonly int a=8;
static void Main()
{
a = 10;
Console.WriteLine(a);
Console.ReadKey();
}
}
}
//Output Error 1
A static readonly field cannot be assigned to (except in a static constructor
or a variable initializer)
Readonly field
can be declared either at time of declaration or in constructor of same class.
Difference
between const and Readonly keyword
A const field
can only be initialized at the declaration of the field.
A readonly field can be
initialized either at the declaration or in a constructor. Therefore, readonly fields
can have different values depending on the constructor used.
Const field is a compile-time constant whereas Readonly field can be used for runtime constant.
Const field is a compile-time constant whereas Readonly field can be used for runtime constant.
namespace Sample
{
public class Sample1
{
public readonly int _a; //but const field shows error if field not assigned
public Sample1(int a)
{
_a = a;
}
static void Main()
{
Sample1 sample = new Sample1(5);
Console.WriteLine(sample._a);
Console.ReadKey();
}
}
}
//Output 5
