• Both are treated differently @ runtime but same in the compile time, so can’t be overloaded.
• Both are passed by references except ‘ref’ requires that the variable to be initialized before passed.

ref:

class Program
 {
 static void M1(out int i)
 {
 i = 1;
 i += 1;
 }

static void Main(string[] args)
 {
 int j; //Not assigned
 M1(out j);
 Console.Write(j);
 Console.Read();
 }
 }
}

The output is : 2

out:

class Program
 {
 static void M1(ref int i)
 {
 i = 1;
 i += 1;
 }

 static void Main(string[] args)
 {
 int j=0; //Assigned
 M1(ref j);
 Console.Write(j);
 Console.Read();
 }
}

The output is same: 2, but we have to assigned the variable before used otherwise we will get an error.