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ref and out are parameter modifiers in C# that allow a method to pass values by reference. The main difference is that a ref parameter must be initialized before it is passed, while an out parameter does not need to be initialized before being passed.

ref is used when a method needs to read and modify an existing value.
out is used when a method needs to return a value through a parameter.

Example: Program to demonstrate how ref modifies an existing variable, while out assigns a value to a variable through a method parameter.

CSharp

using System;

class GFG {

    // Main method
    static public void Main()
    {

        // Declaring variable
        // without assigning value
        int G;

        // Pass variable G to the method
        // using out keyword
        Sum(out G);

        // Display the value G
        Console.WriteLine("The sum of" + 
                " the value is: {0}", G);
    }

    // Method in which out parameter is passed
    // and this method returns the value of
    // the passed parameter
    public static void Sum(out int G)
    {
        G = 80;
        G += G;
    }
}

Output

The sum of the value is: 160

Explanation: The ref parameter a must be initialized before calling the method, while the out parameter b does not need to be initialized. Both methods modify the original variables.

ref Keyword

The ref keyword is used to pass a parameter by reference. It allows the method to work directly with the original variable, so changes made inside the method affect the original value.

The variable must be initialized before passing it with ref.
The ref keyword must be used in both the method declaration and method call.

Example: The ref parameter changes the original variable from 50 to 100.

using System;

class GFG
{
    static void ChangeValue(ref int x)
    {
        x = 100;
    }

    static void Main()
    {
        int num = 50;

        ChangeValue(ref num);

        Console.WriteLine(num);
    }
}

Output

out Keyword

The out keyword is used to pass a parameter by reference when a method needs to return a value through that parameter. The variable does not need to be initialized before it is passed.

The variable does not need to be initialized before passing it with out.
The method must assign a value to the out parameter before it returns.

Example: The out parameter assigns the value 100 to num.

using System;

class GFG
{
    static void GetValue(out int x)
    {
        x = 100;
    }

    static void Main()
    {
        int num;

        GetValue(out num);

        Console.WriteLine(num);
    }
}

Output

Difference between Ref and Out keywords

Feature	ref Keyword	out Keyword
Purpose	Allows a method to access and modify an existing variable.	Allows a method to assign a value to a variable.
Initialization	Variable must be initialized before passing it.	Variable does not need to be initialized before passing it.
Assignment Inside Method	Assigning a new value is optional.	Method must assign a value before returning normally.
Accessing Value	Method can read the existing value immediately.	Method cannot read the parameter before assigning it.
Value Modification	Changes made inside the method affect the original variable.	Value assigned inside the method is stored in the original variable.
Common Use Case	Modifying an existing value.	Returning additional values from a method.
Example	Update(ref num)	GetValue(out num)

Difference between Ref and Out keywords in C#

ref Keyword

out Keyword

Difference between Ref and Out keywords

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