What is the purpose of a ref parameter in C#?

In C#, the purpose of a ref parameter is to allow passing a reference of a parameter during a method call. Declaring a parameter with the ref keyword allows for modifying the value of the passed parameter within the method, and this change will be reflected outside the method.

Specifically, the ref parameter is used in the following situations:

1. When you need to modify the value of a parameter inside a method, you can use a ref parameter. Typically, in C#, methods pass parameters by value, meaning that modifying the parameter inside the method does not affect the variable outside the method. However, by using a ref parameter, modifying the parameter inside the method will change the variable outside the method.
2. When multiple results need to be returned by a method, ref parameters can be used. By declaring the parameter as a ref type, the value of the parameter can be modified within the method, and these modifications will be reflected outside the method after the method call ends.

It is important to note that when calling a method with a ref parameter, the passed argument must be an already initialized variable, and not a literal or uninitialized variable. Additionally, the ref parameter must be initialized at the time of the method call, or else a compilation error will occur.