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

Ref Parameter

A reference parameter is a reference to a memory location of a variable. When you pass parameters by reference, unlike value parameters, a new storage location is not created for these parameters.

You can declare the reference parameters using the ref keyword. The following is an example −

Example

 Live Demo

using System; namespace CalculatorApplication {    class NumberManipulator {       public void swap(ref int x, ref int y) {          int temp;          temp = x; /* save the value of x */          x = y; /* put y into x */          y = temp; /* put temp into y */       }       static void Main(string[] args) {          NumberManipulator n = new NumberManipulator();          /* local variable definition */          int a = 100;          int b = 200;                Console.WriteLine("Before swap, value of a : {0}", a);          Console.WriteLine("Before swap, value of b : {0}", b);          /* calling a function to swap the values */          n.swap(ref a, ref b);          Console.WriteLine("After swap, value of a : {0}", a);          Console.WriteLine("After swap, value of b : {0}", b);          Console.ReadLine();       }    } }

Output

Before swap, value of a : 100 Before swap, value of b : 200 After swap, value of a : 200 After swap, value of b : 100

Out Parameter

A return statement can be used for returning only one value from a function. However, using out parameter, you can return two values from a function.

The following is an example −

Example

 Live Demo

using System; namespace CalculatorApplication {    class NumberManipulator {       public void getValue(out int x ) {          int temp = 10;          x = temp;       }       static void Main(string[] args) {          NumberManipulator n = new NumberManipulator();          /* local variable definition */          int a = 150;          Console.WriteLine("Before method call, value of a : {0}", a);          /* calling a function to get the value */          n.getValue(out a);          Console.WriteLine("After method call, value of a : {0}", a);          Console.ReadLine();       }    } }

Output

Before method call, value of a : 150 After method call, value of a : 10