Ref, Out, In Parameters

Ref, Out and In keywords in C# are used to pass arguments within a method or function. These keywords indicate that an argument/parameter is passed by reference. The normal parameter what we studied before is passed by value. In order to declare Ref, out and in parameter, we need to go before parameters and use ref, out or in keyword.
Before C# version 7.2, there are only ref and out keywords for passing the references of a variable. Out is meant for output only whereas ref is meant for both input and output. However, if we had to pass a read-only reference, i.e., passing a variable as input only, then there was no direct option for that. So, in C# 7.2, in parameter has been introduced.

Call by value or value type - Assigning the value of one variable to another.
Call by reference or reference type - Referring the memory location of one variable to another.

So far we created lot of methods with parameters. We haven't used ref, out or in keyword before any parameters hence all those parameters are called as normal parameters. All ref, out and in parameters are call by reference type. Now we going to see how system will work if we use ref, out and in parameter. But before studying that we need to know the difference between these 3 parameters. Apart from the difference what mentioned below all 3 ref, out, in Parameter work in a same way.

ref parameter - The method having ref parameter may or may not assign the value of that parameter.
out parameter - The method having out parameter must assign the value of that parameter.
in parameter - The method having in parameter cannot assign the value of that parameter(it will be Read only).

CODE

EG 1 . Creating a method with ref parameters

class Program {
    static void Addition(ref int number1, ref int number2) {
        //Addition method may or may not assign the value of ref parameters
        Console.WriteLine(number1 + number2);
    }
    static void Main(string[] args) {
        //Referring the memory of num1 and num2 of main method to number1 and number2 of Addition method.
        int num1 = 5, num2 = 6;
        Addition(ref num1,ref num2);
    }
}

OUTPUT
11

Call by referrence or Reference type memory allocation

CODE EXPLANATION
In the above code, we created Addition method with 2 ref parameters. Since ref parameter is reference type while invoking Addition method we cannot directly pass arguments, we need to refer memory of another variable so we created 2 variables in main method called num1, num2. We referred the memory location of num1 and num2 of main method to number1 and number2 of Addition method respectively. Just because we shared the memory location both num1 of main method and number1 of addition method going to share the same memory. num2 of main method and number2 of addition method going to share the same memory(Refer above visual diagram). If number1 value changes automatically that'll change num1 value. If number2 value changes automatically that'll change num2 value.


EG 2 . Creating a method with out parameters

class Program {
    static void Addition(out int number1, out int number2) {
        //Addition method must assign the value of out parameters
        number1 = 17; number2 = 9;
        Console.WriteLine(number1 + number2);
    }
    static void Main(string[] args) {
        //It doesn't make any sense assigning num1 and num2 values here because value assigned in Addition method will only taken.
        int num1 = 5, num2 = 6;
        Addition(out num1,out num2);
    }
}

OUTPUT
26

CODE EXPLANATION
The function of out parameter is same as that of ref parameter. The only difference between ref and out parameter is, If a method having out parameters that method must assign the value of those out parameters whereas in ref parameter if we want we can assign the values or else we can leave as it is. Just because method having out parameter itself is going to assign the value of out parameters, it doesn't make any sense assigning num1 and num2 values in main method. The value assigned inside Addition method will only be taken.


EG 3 . Creating a method with in parameters

class Program {
    static void Addition(in int number1, in int number2) {
        //Addition method cannot assign the value of in parameters
        Console.WriteLine(number1 + number2);
    }
    static void Main(string[] args) {
        //While invoking we must assign the value of in paramters number1 and number2.
        int num1 = 5, num2 = 6;
        Addition(in num1,in num2);
    }
}

OUTPUT
11

CODE EXPLANATION
The function of in parameter is same as that of ref and out parameter. The only difference is, If a method having in parameter that method cannot assign the value of those in parameters because in parameters are read only parameters. While invoking method with in parameter it is mandatory to assign values of in parameters.


What is the advantage of using Ref, Out and In parameter?
We already studied that void method does not return any value but using this call by reference parameters we can make void method return value.
We'll take the above EG 1 , We created void method called Addition inside we created 2 ref parameters called number1 and number2. This number1 and number2 are going to share the same memory with num1 and num2 of main method. So if number1 and number2 value inside void method changes that'll automatically impact num1 and num2 values of main method. so using this ref, out and in we can make void method return values (Return is not the exact term what we need to use here. In order to understand we are using return word).

Exercises
1. Write a function void simpleMath(double number, ref double square, out double cube). Here square should return square value of number. cube should return cube value of number.

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