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.

Pass by Reference (ref & out) Need to assign an initial value to the parameter out No need to assign an initial value to the parameter static void FunctionOutRef(ref int c, out int d) { d = c + 1; c = c + 1; } static void Main(string[] args) int num3 = 5, num4; FunctionOutRef(ref num3, out num4);

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 copy value copy value main function 10 15

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) 15 refers to the same memory location copy value main function 10 15

Example: Swap Write a function that swaps the values of its two integer parameters

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 Sometimes very useful provides self documentation re-use the same value across the class or program avoid accidental value changes Like variables, but their value is assigned at declaration and can never change afterwards declared by using const before the type name (any type is OK) public const double PI = 3.14159; const int LENGTH = 6; later you can use their value Console.WriteLine(MathClass.PI * 4 * 4); but cannot change their value MathClass.PI = 3.14; causes a syntax error

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; }

struct (structure) struct is very similar to a class Like classes, struct’s can have methods and properties with access modifiers. Struct members are accessed via (.) operator similarly. So they are almost the same with one difference: Class is a reference type whereas struct is a value type. Example: mystruct.cs