What are the differences between ref and out keywords in C#?

In C#, both ref and out keywords are used to pass arguments to methods by reference rather than by value. However, there are differences in how they are used and how they behave:

ref Keyword:

• The ref keyword is used to indicate that a parameter is passed by reference to the method.
• The parameter must be initialized before it is passed to the method.
• The method can read and modify the parameter's value.
• The value passed to the method must be initialized before the method is called.
• ref parameters must be explicitly marked as ref both in the method signature and during the method call.
• The value of the parameter passed to the method can be changed inside the method and the changes persist after the method call.

Here's an example demonstrating the usage of the ref keyword:

class Program
{
    static void Main(string[] args)
    {
        int number = 10;
        Console.WriteLine("Before calling the method: " + number); // Output: Before calling the method: 10

        ModifyNumber(ref number);

        Console.WriteLine("After calling the method: " + number); // Output: After calling the method: 20
    }

    static void ModifyNumber(ref int num)
    {
        num = num * 2;
    }
}

out Keyword:

• The out keyword is similar to the ref keyword, but it is used to indicate that a parameter is being used to return a value from the method rather than just being passed by reference.
• Unlike ref parameters, out parameters do not need to be initialized before they are passed to the method. However, they must be assigned a value inside the method before the method returns.
• out parameters must be explicitly marked as out both in the method signature and during the method call.
• The value passed to the method doesn't need to be initialized before the method is called; it can be declared and passed directly.

Here's an example demonstrating the usage of the out keyword:

class Program
{
    static void Main(string[] args)
    {
        int result;
        Calculate(10, 5, out result);
        Console.WriteLine("Result: " + result); // Output: Result: 15
    }

    static void Calculate(int a, int b, out int sum)
    {
        sum = a + b;
    }
}

In summary, both ref and out keywords allow methods to modify the values of parameters passed to them. However, ref is used for passing initialized variables by reference, while out is used for returning values from a method.