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BİL527 – Bilgisayar Programlama I

BİL527 – Bilgisayar Programlama I. Strings. Contents. More on Variables Type Conversions Enumerations Structs Arrays String Operations. Type Conversion. Examples string to int or int to string double to int (rounding operations) Implicit Conversions No data loss

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BİL527 – Bilgisayar Programlama I

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  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

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