C # difference between const and readonly modifier,

C # difference between const and readonly modifier,

The concept of const is a variable that contains unchangeable values.
Constant expressions are fully computed during compilation. Therefore, constants cannot be initialized by extracting values from a variable.
If const int a = B + 1; B is a variable, it is obvious that the result cannot be calculated during compilation, so constants cannot be initialized using variables.

Readonly allows a field to be set as a constant, but some operations can be performed to determine its initial value.
Because readonly is executed during computing, of course it can be initialized with some variables.
Readonly is an instance Member, so different instances can have different constant values, which makes readonly more flexible.

The readonly keyword is different from the const keyword.

1. the const field can only be initialized in the declaration of this field.
The readonly field can be initialized in the Declaration or constructor. Therefore, the readonly field may have different values based on the constructors used.
2. the const field is the number of compiling times, while the readonly field can be used for running times.
3. const is static by default, and readonly must display the declaration if it is set to static.
4. For constants of the reference type, the possible values of const can only be string and null.
Readonly can be of any type

Summary
The const field can only be initialized in the declaration of this field
The readonly field can be initialized in the Declaration or constructor.
Therefore, the readonly field may have different values based on the constructors used.