Difference between const and readonly in c#.net

1. Compile time only const property value will set. It will not change at runtime.
2. Bascially, constants are static in nature.
3. we should declare constants with in the funcations.
4. We can use this one as attribute.
5. When you refer constant from one assembly to other, value will compiled into the calling assembly. If you try to update the constant value in the referenced assembly it won't change.
6. Const can't be marked as static.

1. At Runtime readonly field will evaluate.
2. We can change the readonly value at runtime. But we can't change the structure of the array. Please check below example 2.It will mark the field as unchangeable.
3. It will not execute at compile time
3. Most of the time we will use this readonly in the constructors for assignments. Please refer example1 and image.


public class ConstAndReadOnly
  public const int iVALUE = 6;
  public readonly int iReadOnly;
  public ConstAndReadOnly()
     iReadOnly= 3;


    class ReadonlyChangeMethod
        public const string CONSTANTVALUE = "Ranga RAjesh";
        public readonly string[] TOWNS = new string[] { "HYDERABAD", "BANGALORE" };

        public string UpdateReadonlyField()
            TOWNS[0] = "Mumbai";
            return TOWNS[0];

    class ReadonlyVsConst
        static void Main(string[] args)
            ReadonlyChangeMethod obj = new ReadonlyChangeMethod();

    //Output: Mumbai

Difference between readonly and const in c#

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