Method Parameters in C#

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When method with parameters is called, you need to pass the parameters to the method. In C#, there are 4 ways that parameters can be passed to a method:

Mechanism	Description
Value parameters	Create a copy of the parameters passed, So modification doesn't effect each other.
Reference parameters	This method copies the reference to the memory location of an argument into the formal parameter. This means that changes made to the parameter affect the argument.
Output parameters	This method helps in returning more than one value.
Parameter array	It use "params" Keyword.

Value Parameters :-

The values of the actual parameters are copied into them. So, the changes made to the parameter inside the method have no effect on the argument. The following example demonstrates the concept:

using System;

namespace CalculatorApplication
{
    class NumberManipulator
    {
        public void swap(int x, 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(a, b);

            Console.WriteLine("After swap, value of a : {0}", a);
            Console.WriteLine("After swap, value of b : {0}", b);
 
            Console.ReadLine();
        }
    }
}

When the above code is compiled and executed, it produces the following result:

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

It shows that there is no change in the values though they had been changed inside the function.

Reference parameters

A reference parameter is a reference to a memory location of a variable. When you pass parametersby reference, unlike value parameters, a new storage location is not created for these parameters. The reference parameters represent the same memory location as the actual parameters that are supplied to the method.

In C#, you declare the reference parameters using the ref keyword. The following example demonstrates this:

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();

      }
   }
}

When the above code is compiled and executed, it produces the following result:

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

It shows that the values have been changed inside the swap function and this change reflects in theMain function.

Output parameters

A return statement can be used for returning only one value from a function. However, using output parameters, you can return two values from a function. Output parameters are like reference parameters, except that they transfer data out of the method rather than into it.

The following example illustrates this:

using System;

namespace CalculatorApplication
{
   class NumberManipulator
   {
      public void getValue(out int x )
      {
         int temp = 5;
         x = temp;
      }
   
      static void Main(string[] args)
      {
         NumberManipulator n = new NumberManipulator();
         /* local variable definition */
         int a = 100;
         
         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();

      }
   }
}

When the above code is compiled and executed, it produces the following result:

Before method call, value of a : 100
After method call, value of a : 5

The variable supplied for the output parameter need not be assigned a value the method call. Output parameters are particularly useful when you need to return values from a method through the parameters without assigning an initial value to the parameter. Look at the following example, to understand this:

using System;

namespace CalculatorApplication
{
   class NumberManipulator
   {
      public void getValues(out int x, out int y )
      {
          Console.WriteLine("Enter the first value: ");
          x = Convert.ToInt32(Console.ReadLine());
          Console.WriteLine("Enter the second value: ");
          y = Convert.ToInt32(Console.ReadLine());
      }
   
      static void Main(string[] args)
      {
         NumberManipulator n = new NumberManipulator();
         /* local variable definition */
         int a , b;
         
         /* calling a function to get the values */
         n.getValues(out a, out b);

         Console.WriteLine("After method call, value of a : {0}", a);
         Console.WriteLine("After method call, value of b : {0}", b);
         Console.ReadLine();
      }
   }
}

When the above code is compiled and executed, it produces the following result (depending upon the user input):

Enter the first value:
7
Enter the second value:
8
After method call, value of a : 7
After method call, value of b : 8

Parameter array

It use "param" keyword

using System;

   class Programme
   {
      public static void ParamsMethod(params int[] Numbers)
      {
          Console.WriteLine("there are {0} element ":, numbers.length);
          foreach ( int i in numbers)
          Console.WriteLine(i);                                                  
          } 
      }
   }                                                                                        public static void Main()
      {
         Number[0] = 101
         Number[1] = 102         Number[2] = 103
         ParamsMethod(1,2,3,4,5);// param method or param method(number)
         }
         
        
      }
   }
}

we can not use    "public static void ParamsMethod(params int[] Numbers, Int number) because param keyword should be last keyword.
we can not use    "public static void ParamsMethod(params int[] Numbers, Params number) because param keyword should be one.



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