Understanding Pass by Reference, const, readonly and struct in C#, Slides of Information Security and Markup Languages

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Pass by Reference,

const, readonly, struct

Pass by Reference Parameters

 The parameters we have seen so far are value parameters

 their arguments are passed by value

 if you change the value of a parameter in function, corresponding

argument does NOT change in the caller function

 Let’s see an example: PassByRef.cs.

Underlying Mechanisms

• For value parameters, the arguments’ values are

copied into parameters

• arguments and parameters have different memory locations double Average (int a, int b) Average(num1, num2) 10 15 10 15 copy value (^) copy value main function

Underlying Mechanisms

 For reference parameters, the parameter and the

argument share the same memory location

 parameter is an alias of argument double average (ref int a, int b) average(ref num1, num2) 10 15 15 refers to the same memory location copy value main function

Example: Swap

void swap(ref int a, ref int b) { int temp; temp = a; a = b; b = temp; }

• How do we use this in main? int a=5, b=8; swap(ref a, ref b); // a becomes 8, b becomes 5 swap(ref a, ref 5); // syntax error, arguments must be variables

Passing Arrays as Parameters

 To pass an array argument to a method, specify the name of the

array without any brackets. For a method to receive an array

reference through a method call, the method’s parameter list must

specify an array parameter.

 When an argument to a method is an entire array or an individual

array element of a reference type, the called method receives a

copy of the reference.

 When an argument to a method is an individual array element of a

value type, the called method receives a copy of the element’s

value.

 To pass an individual array element to a method, use the indexed

name of the array as an argument in the method call.

 Example: ArrayReferenceTest.cs

const

• Cannot use const with reference types.
• Exception: string public const string CLASSNAME = “IT 528”;

readonly

 const is set at compile time

 readonly is set at runtime

 readonly can be used for reference types as

well

 Constructor can set readonly fields but not

any other methods

public class GradeBook { private readonly string courseName = “”; public GradeBook(string name) { courseName = name; } }