1. BİL527 – Bilgisayar Programlama I
Functions

2. Contents
Functions

3. Functions
Some tasks may need to be performed at several points in a program
e.g. finding the highest number in an array
Solution: Write the code in a function and call it several times
In object-oriented programming languages, functions of objects are named as methods

4. Don’t forget to use the word ‘static’!
Function Example
class Program { static void DrawBorder() Console.WriteLine(“ ”); } static void Main(string[] args) DrawBorder(); Console.WriteLine(“| Hello! |”);
| Hello! |
Don’t forget to use the word ‘static’!

5. Functions that return a value
static int ReadAge() { Console.Write(“Enter your age: ”); int age = int.Parse(Console.ReadLine()); if (age < 1) return 1; else if (age > 120) return 120; else return age; }

6. Functions that take parameters
static double Product(double a, double b) { return a * b; }

7. Functions that take array as parameter
class Program { static int MaxValue(int[] intArray) { int maxVal = intArray[0]; for (int i = 1; i < intArray.Length; i++) { if (intArray[i] > maxVal) maxVal = intArray[i]; } return maxVal; static void Main(string[] args) { int[] myArray = { 1, 8, 3, 6, 2, 5, 9, 3, 0, 2 }; int maxVal = MaxValue(myArray); Console.WriteLine("The maximum value in myArray is {0}", maxVal);

8. Parameter Arrays
If your function may take variable amount of parameters, then you can use the parameter arrays
Think of Console.WriteLine(format, params)
You can use any amount of parameters after the format string
Parameter arrays can be declared with the keyword params
Parameter array should be the last parameter in the parameter list of the function

9. params Example
class Program { static int SumVals(params int[] vals) { int sum = 0; foreach (int val in vals) { sum += val; } return sum; static void Main(string[] args) { int sum = SumVals(1, 5, 2, 9, 8); Console.WriteLine("Summed Values = {0}", sum);

10. Call By Value and Call By Reference
If you change a value-type parameter in the function, it doesn’t affect the value in the main function
because, only the value is transferred
However, if you change a reference-type parameter’s elements, then the argument in the main function is also changed
because the object itself is transferred
You can think arrays as reference-types

11. Call By Value val doubled = 10 myNumber in main: 5
static void ShowDouble(int val) { val *= 2; Console.WriteLine(“val doubled = {0}”, val); } static void Main(string[] args) { int myNumber = 5; ShowDouble(myNumber); Console.WriteLine(“myNumber in main: ” + myNumber);
val doubled = 10
myNumber in main: 5

12. Call By Reference
static void ChangeFirst(int[] arr) { arr[0] = 99; } static void Main(string[] args) int[] myArr = {1, 2, 3, 4, 5}; DisplayArray(myArr); ChangeFirst(myArr);

13. ref and out
You can change the value of argument in the Main function via a function using the ref keyword
You can declare a parameter as the output of a function with the out keyword
out parameters does not have to be initialized before the function call (their values are set by the function)

14. ref Example val doubled = 10 myNumber in main: 10
static void ShowDouble(ref int val) { val *= 2; Console.WriteLine(“val doubled = {0}”, val); } static void Main(string[] args) { int myNumber = 5; ShowDouble(ref myNumber); Console.WriteLine(“myNumber in main: ” + myNumber);
val doubled = 10
myNumber in main: 10

15. out Example
static void FindAvgAndSum(int[] arr, out double avg, out int sum) { sum = 0; foreach (int num in arr) { sum += num; } avg = (double) sum / arr.Lenght; static void Main(string[] args) { int sum; double avg; int[] myArray = {3, 4 , 8, 2, 7}; FindAvgAndSum(myArray, out avg, out sum);

16. Another Example for out
static int MaxValue(int[] intArray, out int maxIndex) { int maxVal = intArray[0]; maxIndex = 0; for (int i = 1; i < intArray.Length; i++) { if (intArray[i] > maxVal) { maxVal = intArray[i]; maxIndex = i; } return maxVal;

17. Variable Scope
Variables in a functions are not accessible by other functions
they are called local variables
The variables declared in the class definition are accessible by all functions in the class
they are called global variables
they should be static so that static functions can access them
Variables declared in a block (for, while, {}, etc.) are only accessible in that block

18. The Main Function The Main function is the entry point in a C# program
It takes a string array parameter, whose elements are called command-line parameters
The following declarations of Main are all valid:
static void Main()
static void Main(string[] args)
static int Main()
static int Main(string[] args)

19. Command-Line Parameters
class Program { static void Main(string[] args) Console.WriteLine("{0} command line arguments were specified:", args.Length); foreach (string arg in args) Console.WriteLine(arg); }

20. Specifying Command-Line Arguments in Visual Studio
Right-click on the project name in the Solution Explorer window and select Properties
Select the Debug pane
Write command-line arguments into the box
Run the application

21. Specifying Command-Line Arguments in Command Prompt
Open a command prompt
Go to the folder of the executable output of the program
Write the name of the executable followed by the command-line arguments
prog.exe 256 myfile.txt “a longer argument”

22. struct Functions
struct CustomerName { public string firstName, lastName; public string Name() return firstName + " " + lastName; }

23. Calling struct Function
CustomerName myCustomer; myCustomer.firstName = "John"; myCustomer.lastName = "Franklin"; Console.WriteLine(myCustomer.Name());

24. Overloading Functions
A function may have several signatures
i.e. same function name but different parameters
e.g. Console.WriteLine()
Intellisense feature of the Visual Studio helps us to select the correct function

25. Example 1
static int MaxValue(int[] intArray) { … } static double MaxValue(double[] doubleArray) { static void Main(string[] args) { int[] arr1 = { 1, 8, 3, 6, 2, 5, 9, 3, 0, 2 }; double[] arr2 = { 0.1, 0.8, 0.3, 1.6, 0.2}; int maxVal1 = MaxValue(arr1); double maxVal2 = MaxValue(arr2);