BİL527 – Bilgisayar Programlama I

Strings

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Contents

• More on Variables– Type Conversions– Enumerations– Structs– Arrays– String Operations

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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

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Implicit Conversions

• Implicit conversion requires no work on your part and no additional code.

• ushort and char types are effectively interchangeable, because both store a number between 0 and 65535.

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Implicit Conversion Example

char ch = ‘a’;ushort num;num = ch;Console.WriteLine(“ch = {0}, num = {1}”, ch, num);

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ch = a, num = 97

Implicit Type ConversionsType Can Safely Be Converted Tochar ushort, int, uint, long, ulong, float, double, decimalbyte short, ushort, int, uint, long, ulong, float, double, decimalsbyte short, int, long, float, double, decimalshort int, long, float, double, decimalushort int, uint, long, ulong, float, double, decimalint long, float, double, decimaluint long, ulong, float, double, decimallong float, double, decimalulong float, double, decimalfloat doubledouble -decimal -

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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.

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Example

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

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Cannot implicitly convert type ‘short’ to ‘byte’. An explicit conversion exists(are you missing a cast?)

Solution

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

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b = 7, s = 7

Range Problem

byte b;short s = 281;b = (byte) s;Console.WriteLine(“b = {0}, s = {1}”, b, s);

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b = 25, s = 281

281 doesn’t fit into the byte range!

Amount of overflow from 256!

Explicit Conversions by “Convert”

• Another method to make explicit conversion is using the “Convert” methods:– int i = 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.

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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);

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Complex Variable Types

• Enumerations (enum)• Structures (struct)• Arrays

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Enumerations (enum)

• The type double is used to store fractional numbers• bool type is used to store true or 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 enumerations in C#.

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enum Syntax

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

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enum Syntax

• Declaring variables:<typeName> <varName>;

• Assigning values:<varName> = <typeName>.<value>;

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

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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);

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North = 0, South = 1

Advanced Topics on enum (2)

• You can change underlying integer values of some enumerations

• Unspecified values are automatically generated by incrementing last valueenum Orientation {North=1, South, East=4, West=8}

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North = 1, South = 2,East = 4, West = 8

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)

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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.)

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Defining Structs

struct <structName>{ <accessibility1> <type1> <name1>; <accessibility2> <type2> <name2>; …}

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Example

struct Route{ public Orientation Direction; public double Distance;}

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Declaring a struct variable

Syntax:<structName> <varName>;

Example:Route myRoute;myRoute.Orientation = Orientation.North;myRoute.Distance = 2.5;

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Exampleroute myRoute;int myDirection = -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);

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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.

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Declaring Arrays

• Syntax:<type>[] <name>;

• Example:– int[] myIntArray;– string[] myStringArray;

• In this declaration, only a reference without any elements is created

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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)

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Accessing Array Elements

arr[5] = 10;– 10 is assigned to the 6th element of the array– Indexing starts from 0 (not 1)

int num = arr[5];– 6th element of the array is assigned to a variable

for (int i = 0; i < arr.Length; i++){ Console.WriteLine(arr[i]);}– All array elements are displayed on the screen.

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Example

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

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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);}

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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)

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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();

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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();

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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”

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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 spacesstring str = “This is a pencil”;string[] arr = str.Split();foreach (string s in arr){ Console.WriteLine(s);}

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Thisisapencil

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);}

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12345

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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