BİL527 – Bilgisayar Programlama I

1. BİL527 – Bilgisayar Programlama I Strings

2. Contents • More on Variables • Type Conversions • Enumerations • Structs • Arrays • String Operations

3. Type Conversion • Examples • string to int or int to string • double to int (rounding operations) • Implicit Conversions • No data loss • Trust in the compiler • Explicit Conversions • Data may be lost • Approve the compiler

4. Implicit Conversions • Implicit conversion requires no work on your part and no additional code. • ushortand chartypes are effectively interchangeable, because both store a number between 0 and 65535.

5. Implicit Conversion Example char ch = ‘a’; ushortnum; num= ch; Console.WriteLine(“ch = {0}, num = {1}”, ch, num); ch = a, num = 97

6. Implicit Type Conversions

7. Explicit Conversions • Wide types can’t be converted to narrow types (e.g. conversion from short to byte) • In such cases, compiler gives error: • Cannot implicitly convert type ‘short’ to ‘byte’. An explicit conversion exists (are you missing a cast?) • If you are sure that you really want to make the conversion, use the explicit conversion: • OK, I know you’ve warned me about doing this, but I’ll take responsibility for what happens.

8. Example byte b; short s = 7; b = s; Console.WriteLine(“b = {0}, s = {1}”, b, s); Cannot implicitly convert type ‘short’ to ‘byte’. An explicit conversion exists (are you missing a cast?)

9. Solution byte b; short s = 7; b = (byte) s; Console.WriteLine(“b = {0}, s = {1}”, b, s); b = 7, s = 7

10. Range Problem 281 doesn’t fit into the byte range! byte b; short s = 281; b = (byte) s; Console.WriteLine(“b = {0}, s = {1}”, b, s); b = 25, s = 281 Amount of overflow from 256!

11. Explicit Conversions by “Convert” • Another method to make explicit conversion is using the “Convert” methods: • inti = Convert.ToInt32(val) • float f = Convert.ToSingle(val) • double d = Convert.ToDouble(val) • string s = Convert.ToString(val) • Here, val can be most types of variable.

12. A Note on Explicit Conversions • If the explicit conversion is impossible, then your program is not compiled. • string s = “12.34”; • double d = (double)s; • If the explicit conversion is possible but an error occurs in runtime, then an Exception occurs (i.e. your program crashes ) • string s = “abcd”; • double d = Convert.ToDouble(s);

13. Complex Variable Types • Enumerations (enum) • Structures (struct) • Arrays

14. Enumerations (enum) • The type doubleis used to store fractional numbers • booltype is used to store trueor false • In real life, there are other existences: • Orientation: North, South, East, West • Week Days: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday • Months: January, February, …, December • These types can be implemented by enumerationsin C#.

15. enum Syntax • Definition: enum <typeName> { <value1>, <value2>, … <valueN> }

16. enum Syntax • Declaring variables: <typeName> <varName>; • Assigning values: <varName> = <typeName>.<value>;

17. enum Example namespace Ch05Ex02 { enumOrientation { North, South, East, West } class Program { static void Main(string[] args) { OrientationmyDirection = Orientation.North; Console.WriteLine("myDirection = {0}", myDirection); } } }

18. Advanced Topics on enum (1) • Each values in an enumeration are stored as integers, starting from 0 and incremented by 1 • Console.WriteLine("{0} = {1}, {2} = {3}", Orientation.North, (int)Orientation.North, Orientation.South, (int)Orientation.South); North = 0, South = 1

19. Advanced Topics on enum (2) • You can change underlying integer values of some enumerations • Unspecified values are automatically generated by incrementing last value enum Orientation {North=1, South, East=4, West=8} North = 1, South = 2, East = 4, West = 8

20. Advanced Topics on enum (3) • You can change the underlying type from the default type (int) to byte, short, and long(and their signed and unsigned versions) enum Orientation : byte {North, South, East, West} Console.WriteLine((byte)Orientation.North)

21. Structs • Structs are data structures that are composed of several pieces of data, possibly of different types. • Student records (name, age, birth year, etc.) • Route (orientation, distance, etc.)

22. Defining Structs struct <structName> { <accessibility1> <type1> <name1>; <accessibility2> <type2> <name2>; … }

23. Example struct Route { public Orientation Direction; public double Distance; }

24. Declaring a struct variable Syntax: <structName> <varName>; Example: Route myRoute; myRoute.Orientation = Orientation.North; myRoute.Distance = 2.5;

25. Example route myRoute; intmyDirection = -1; double myDistance; Console.WriteLine("1) North\n2) South\n3) East\n4) West"); do { Console.WriteLine("Select a direction:"); myDirection = Convert.ToInt32(Console.ReadLine()); } while (myDirection < 1 || myDirection > 4); Console.WriteLine("Input a distance:"); myDistance = Convert.ToDouble(Console.ReadLine()); myRoute.direction = (orientation)myDirection; myRoute.distance = myDistance; Console.WriteLine("myRoute specifies a direction of {0} and a " + "distance of {1}", myRoute.direction, myRoute.distance);

26. Arrays • Use arrays to store large number of data of same type • int grade1, grade2, grade3, …; • int[] grades; • Arrays make some operations simple • Think of the case where you want to initialize all values to zero.

27. Declaring Arrays • Syntax: <type>[] <name>; • Example: • int[] myIntArray; • string[] myStringArray; • In this declaration, only a reference without any elements is created

28. Initialization • int[] arr= new int[5]; • an array of 5 elements with default values (0 for numbers) • int[] arr = {5, 9, 10, 2, 99}; • an array of 5 elements with initial values • int[] arr = new int[5] {5, 9, 10, 2, 99}; • an array of 5 elements with initial values • int[] arr= new int[10] {5, 9, 10, 2, 99}; • an array of 10 elements but only first five of them are initialized (the rest are initialized to the default value)

29. Accessing Array Elements arr[5] = 10; • 10 is assigned to the 6th element of the array • Indexing starts from 0 (not 1) intnum = arr[5]; • 6th element of the array is assigned to a variable for (inti = 0; i < arr.Length; i++) { Console.WriteLine(arr[i]); } • All array elements are displayed on the screen.

30. Example string[] friendNames = { "Robert Barwell", "Mike Parry", "Jeremy Beacock" }; Console.WriteLine("Here are {0} of my friends:", friendNames.Length); for (inti = 0; i < friendNames.Length; i++) { Console.WriteLine(friendNames[i]); }

31. Same example with foreach string[] friendNames = { "Robert Barwell", "Mike Parry", "Jeremy Beacock" }; Console.WriteLine("Here are {0} of my friends:", friendNames.Length); foreach (string friendName in friendNames) { Console.WriteLine(friendName); }

32. Multidimensional Arrays • int[,] mat = new int[5, 8]; • Access as mat[i, j] • int[,,] cube = new int[3, 5, 8]; • int[,] mat = {{1,2,3,4},{5,6,7,8},{9,10,11,12}}; • Two-dimensional array of size 3x4 (3 rows, 4 columns)

33. String Operations (1) • Concatenation • str = str1 + str2; • Accessing a char at specified location • char ch = str[3]; // 4th element is assigned to ch • Getting the length • int size = str.Length; • Getting all chars into a char array • char[] chars = str.ToCharArray();

34. String Operations (2) • Changing to upper or lower cases • str2 = str1.ToUpper(); • str2 = str1.ToLower(); • These methods doesn’t change str1! • If you want to change str1 itself, use this: • str1 = str1.ToLower(); • Remove white spaces (space, tab, new line) at the beginning and at the end: • str2 = str1.Trim();

35. String Operations (3) • Remove white spaces only at the beginning: • str2 = str1.TrimStart(); • Remove white spaces only at the end: • str2 = str1.TrimEnd(); • Substrings: • string str1 = “advanced”; • string str2 = str1.SubString(2, 3); // “van” • str2 = str1.SubString(2); // “vanced”

36. Split() • You can split a string using the Split() method • The Split() method returns a string array • It takes separator chars as a char array • If no parameters are supplied, it splits the string according to the white spaces string str = “This is a pencil”; string[] arr = str.Split(); foreach (string s in arr) { Console.WriteLine(s); } This is a pencil

37. Using separators in Split() string str = “1,2,3,4,5”; char[] separator = {‘,’}; string[] arr = str.Split(separator); foreach (string s in arr) { Console.WriteLine(s); } 1 2 3 4 5

38. Other String Operations • Examine the following string methods by yourself: • CompareTo, Equals • Contains • StartsWith, EndsWith • IndexOf, IndexOfAny, LastIndexOf, LastIndexOfAny • PadLeft, PadRight • Remove • Replace