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‘out’ is a keyword in C#, which is used to pass arguments to a method as a reference type. Variables passed to a method as out parameters do not need to be declared or initialized before they are passed to the method call. The called method is required to assign values to the variables of out parameters before the control leaves the called method and before the called method returns any value to the calling method. It is possible to pass multiple out parameters to a method and the method returns multiple values.
Syntax with explanation:
While calling the method using the out parameter, the syntax will be as follows:
Method_name(out data_type variable_name);
Here, Method_name is any user-defined name given to the method, ‘out’ is the keyword used to express that the variable passed to the method is an out parameter, data_type can be any data type of the variable and variable_name is the user-defined name of the variable.
The syntax for the method to be called is as follows:
access_specifier return_type Method_name(out data_type variable_name);
Here, access_specifier can be any access specifier among the five access specifiers supported by C# like a public or private. Then, return_type is the type of data this method returns followed by method name and ‘out’ parameter list.
In C#, ‘out’ keyword works similar to the ‘ref’ and ‘in’ keywords. The difference between ‘out’ and ‘ref’ parameters is that, ‘out’ parameter variables do not need to be initialized before they are passed to a method, the user can declare the ‘out’ parameter variable in the argument list of the method instead of declaring it separately which is called inline declaration of ‘out’ parameter whereas the ‘ref’ parameter variables need to be initialized before they are passed to a method. The inline declared ‘out’ parameters can be accessed in the same block of code.
Code:
using System; namespace ConsoleApp4 { public class Program { public static void Main(string[] args) { //inline declaration of 'out' parameter Display(out int num); Console.WriteLine("Value of variable 'num': {0}", num); Console.ReadLine(); } public static void Display(out int a) { //need to assign value a = 10; a += a; } } }
Output:
Code:
using System; namespace ConsoleApp4 { public class Program { public static void Main(string[] args) { string str = "123456"; int num; //if ‘canParse’ is true; the result of conversion will be stored in ‘num’ bool canParse = Int32.TryParse(str, out num); if (canParse) Console.WriteLine(num); else Console.WriteLine("Could not be parsed."); Console.ReadLine(); } } }
Output:
Given below are the examples of C# Out Parameter:
Example showing multiple ‘out’ parameters passed to a method and then the method returns multiple values.
Code:
using System; namespace ConsoleApp4 { public class Program { public static void Main() { //declaring variables without assigning values float area, perimeter; //passing multiple variables to a method using 'out' keyword Calculate(5, 10, out area, out perimeter); //displaying the result Console.WriteLine("The area of rectangle is: {0}", area); Console.WriteLine("The perimeter of rectangle is: {0}", perimeter); Console.ReadLine(); } //method taking length & breadth & it will return area and perimeter of rectangle public static void Calculate(int length, int breadth, out float area, out float perimeter) { area = length * breadth; perimeter = 2 * (length + breadth); } } }
Output:
Example showing the inline declaration of ‘out’ parameter.
Code:
using System; namespace ConsoleApp4 { public class Program { public static void Main() { //in-line declaration of variables without assigning values Calculate(out int length, out int breadth, out float area); //displaying the values of length, breadth, and area Console.WriteLine("Length of rectangle: " + length); Console.WriteLine("Breadth of rectangle: " + breadth); Console.WriteLine("Area of rectangle: " + area); Console.ReadLine(); } //method taking 'out' parameters and it returns multiple values public static void Calculate(out int l, out int b, out float a) { l = 30; b = 40; a = l * b; } } }
Output:
‘out’ parameter in C# allows users to pass arguments by reference to a method. Variable used as ‘out’ parameter does not require to be initialized before it is passed to a method. The called method should assign value to the out parameter before it returns a value.
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