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