This & readonly

####The this keyword is used inside the class and refers to the current instance of the class, meaning it refers to the current object. ####One of the common uses of this is to distinguish class members from other data, such as local or formal parameters of a method, as shown in the following example:

class Person {
  private string name;
  public Person(string name) {
    this.name = name;
  }
}

####Here, this.name represents the member of the class, whereas name represents the parameter of the constructor. ####Another common use of this is for passing the current instance to a method as parameter: ShowPersonInfo(this);

###The readonly modifier prevents a member of a class from being modified after construction. It means that the field declared as readonly can be modified only when you declare it or from within a constructor. ####For example:

class Person {
  private readonly string name = "John"; 
  public Person(string name) {
    this.name = name; 
  }
}

####If we try to modify the name field anywhere else, we will get an error.

###There are three major differences between readonly and const fields. ####First, a constant field must be initialized when it is declared, whereas a readonly field can be declared without initialization, as in:

readonly string name; // OK
const double PI; // Error

####Second, a readonly field value can be changed in a constructor, but a constant value cannot. ####Third, the readonly field can be assigned a value that is a result of a calculation, but constants cannot, as in:

readonly double a = Math.Sin(60); // OK
const double b = Math.Sin(60); // Error!