Strings and Text Processing Processing and Manipulating Text SoftUni Team Technical Trainers Software University

Table of Contents 1.What is a String? 2.Creating and Using Strings  Declaring, Creating, Reading and Printing 3.Manipulating Strings  Comparing, Concatenating, Searching  Extracting Substrings, Splitting 2

Table of Contents (2) 4.Other String Operators  Replacing Substrings, Deleting Substrings  Changing Character Casing, Trimming 5.Building and Modifying Strings  Why the + Operator is Slow? StringBuilder  Using the StringBuilder Class 3

What Is a String?

 Strings are sequences of characters  Each character is a Unicode symbol string System.String  Represented by the string data type in C# ( System.String )  Example: string str = "Hello, C#"; Hello, C#str 5

6 System.String  Strings are represented by System.String objects in.NET Framework  String objects contain an immutable (read-only) sequence of characters  Strings use Unicode to support multiple languages and alphabets  Strings are stored in the dynamic memory (managed heap)  System.String  System.String is a reference type The System.String Class

7 char[]  String objects are like arrays of characters ( char[] ) String.Length  Have fixed length ( String.Length )  Elements can be accessed directly by index  The index is in the range [0... Length - 1] The System.String Class (2) string str = "Hello!"; int length = str.Length; // length = 6 char ch = str[1]; // ch = 'e' Hello! index = str[index] =

8 Strings – First Example static void Main() { string song = "Stand up, stand up, Balkan Superman."; string song = "Stand up, stand up, Balkan Superman."; Console.WriteLine("song = \"{0}\"", song); Console.WriteLine("song = \"{0}\"", song); Console.WriteLine("song.Length = {0}", song.Length); Console.WriteLine("song.Length = {0}", song.Length); for (int i = 0; i < song.Length; i++) for (int i = 0; i < song.Length; i++) { Console.WriteLine("song[{0}] = {1}", i, song[i]); Console.WriteLine("song[{0}] = {1}", i, song[i]); }}

Strings Live Demo

Creating and Using Strings Declaring, Creating, Reading and Printing

 Several ways of declaring string variables: string  Using the C# keyword string System.String  Using the.NET's fully qualified class System.String  The above three declarations are equivalent Declaring Strings string str1; System.String str2; String str3; 11

Creating Strings null  Before initializing, a string variable has null value  Strings can be initialized by:  Assigning a string literal to the string variable  Assigning the value of another string variable  Assigning the result of operation of type string new string()  Using the string constructor – new string() 12

Creating Strings (2) null  Uninitialized variables have value of null  Assigning a string literal  Assigning from another string variable string str; // str is equal to null string str = "I am a string literal!"; string str2 = str; 13

Creating Strings (3)  Assigning from the result of a string operation char  Using the string constructor with a repeating char char[]  Using the string constructor with a char[] string str = new string('*', 20); string str = new string({ 'h', 'e', 'l', 'l', 'o' }); string str = 42.ToString(); 14

15  Reading strings from the console Console.ReadLine()  Use the method Console.ReadLine() Reading and Printing Strings string s = Console.ReadLine(); Console.Write("Please enter your name: "); string name = Console.ReadLine(); Console.Write("Hello, {0}! ", name); Console.WriteLine("Welcome to our party!");  Printing strings to the console Write() WriteLine()  Use the methods Write() and WriteLine()

Reading and Printing Strings Live Demo

Manipulating Strings Comparing, Concatenating, Searching, Extracting Substrings, Splitting

18  Several ways to compare two strings:  Dictionary-based string comparison  Case-insensitive  Case-sensitive Comparing Strings int result = string.Compare(str1, str2, true); // result == 0 if str1 equals str2 // result < 0 if str1 is before str2 // result > 0 if str1 is after str2 int result = string.Compare(str1, str2, false);

Comparing Strings (2) ==  Equality checking by operator ==  Performs case-sensitive comparison Equals()  Using the case-sensitive Equals() method ==  The same effect like the operator == if (str1 == str2) { …} if (str1.Equals(str2)) { …} 19

20  Finding the first string in a lexicographical order from a given list of strings: Comparing Strings – Example string[] towns = { "Sofia", "Varna", "Plovdiv", "Pleven", "Bourgas", "Rousse", "Yambol" }; "Rousse", "Yambol" }; string firstTown = towns[0]; for (int i = 1; i < towns.Length; i++) { string currentTown = towns[i]; string currentTown = towns[i]; if (string.Compare(currentTown, firstTown) < 0) if (string.Compare(currentTown, firstTown) < 0) { firstTown = currentTown; firstTown = currentTown; }} Console.WriteLine("First town: {0}", firstTown);

Comparing Strings Live Demo

Concatenating Strings  There are two ways to combine strings: Concat()  Using the Concat() method ++=  Using the + or the += operators  Any object can be appended to a string string str = string.Concat(str1, str2); string str = str1 + str2 + str3; string str += str1; string name = "Peter"; int age = 22; string s = name + " " + age; //  "Peter 22" 22

Concatenating Strings – Example string firstName = "Software"; string lastName = "University"; string fullName = firstName + " " + lastName; Console.WriteLine(fullName); // Software University int age = 5; string nameAndAge = "Name: " + fullName + "\nAge: " + age; Console.WriteLine(nameAndAge); // Name: Software University // Age: 5 23

Concatenating Strings Live Demo

25  Finding a character or substring within given string  str.IndexOf(string term) – returns the index of the first occurrence of term in str  Returns -1 if there is no match  str.LastIndexOf(string term) – returns the index of the last occurrence of term in str Searching in Strings string = int firstIndex = // 5 int noIndex = .IndexOf("/"); // -1 string verse = "To be or not to be.."; int lastIndex = verse.LastIndexOf("be"); // 16

Searching in Strings – Example string str = "C# Programming Course"; int index = str.IndexOf("C#"); // index = 0 index = str.IndexOf("Course"); // index = 15 index = str.IndexOf("COURSE"); // index = -1 // IndexOf is case-sensetive. -1 means not found index = str.IndexOf("ram"); // index = 7 index = str.IndexOf("r"); // index = 4 index = str.IndexOf("r", 5); // index = 7 index = str.IndexOf("r", 8); // index = … C# Programming… index = str[index] = 26

Searching in Strings Live Demo

Extracting Substrings  Extracting substrings  str.Substring(int startIndex, int length)  str.Substring(int startIndex) string filename string name = filename.Substring(8, 8); // name is Rila2009 string filename string nameAndExtension = filename.Substring(8); // nameAndExtension is Summer2009.jpg C:\Pics\Rila2005.jpg 28

Extracting Substrings Live Demo

Splitting Strings  To split a string by given separator(s) use the following method:  Example: string[] Split(params char[] separator) string listOfBeers = "Amstel, Zagorka, Tuborg, Becks."; string[] beers = listOfBeers.Split(' ', ',', '.'); Console.WriteLine("Available beers are:"); foreach (string beer in beers) { Console.WriteLine(beer); Console.WriteLine(beer);} 30

Splitting Strings Live Demo

Other String Operations Replacing Substrings, Deleting Substrings, Changing Character Casing, Trimming

Replacing and Deleting Substrings  str.Replace(string match, string term) – replaces all occurrences of given string with another  The result is a new string (strings are immutable)  str.Remove(int index, int length)  str.Remove(int index, int length) – deletes part of a string and produces a new string as result string cocktail = "Vodka + Martini + Cherry"; string replaced = cocktail.Replace("+", "and"); // Vodka and Martini and Cherry string price = "$ "; string lowPrice = price.Remove(2, 3); // $

Changing Character Casing ToLower()  Using the method ToLower() ToUpper()  Using the method ToUpper() string alpha = "aBcDeFg"; string lowerAlpha = alpha.ToLower(); // abcdefg Console.WriteLine(lowerAlpha); string alpha = "aBcDeFg"; string upperAlpha = alpha.ToUpper(); // ABCDEFG Console.WriteLine(upperAlpha); 34

35  str.Trim() – trims whitespaces at start and end of string Trim(params char[] chars)  str.Trim(params char[] chars)  str.TrimStart() and str.TrimEnd() Trimming White Space string s = " example of white space "; string clean = s.Trim(); Console.WriteLine(clean); // example of white space string s = " \t\nHello!!! \n"; string clean = s.Trim(' ', ',','!', '\n','\t'); Console.WriteLine(clean); // Hello string s = " C# "; string clean = s.TrimStart(); // clean = "C# ";

Other String Operations Live Demo

Building and Modifying Strings Using the StringBuilder Class

Constructing Strings  Strings are immutable!  Concat()Replace()Trim()  Concat(), Replace(), Trim(),... return a new string (allocate new piece of memory), do not modify the old one  Do not concatenate strings in loops!  Results in terrible performance. public static string ConcatenateChar(char ch, int count) { string result = string.Empty; string result = string.Empty; for (int i = 0; i < count; i++) for (int i = 0; i < count; i++) { result += ch; } return result; return result;} Very bad practice. Avoid this! 38

Slow Building Strings with + Live Demo

StringBuilder: How It Works?  StringBuilder  StringBuilder keeps a buffer memory, allocated in advance  Most operations use the buffer memory and do not allocate new objectsHello,C#! StringBuilder : Length = 9 Capacity = 15 Capacity used buffer (Length) (Length) unused buffer 40

41 System.Text.StringBuilder  Use the System.Text.StringBuilder class for modifiable strings of characters: StringBuilder  Use StringBuilder if you need to keep adding characters to a string Changing the Contents of a String public static string ReverseString(string s) { StringBuilder sb = new StringBuilder(); StringBuilder sb = new StringBuilder(); for (int i = s.Length - 1; i >= 0; i--) for (int i = s.Length - 1; i >= 0; i--) { sb.Append(s[i]); sb.Append(s[i]); } return sb.ToString(); return sb.ToString();}

The StringBuilder Class  StringBuilder(int capacity)  StringBuilder(int capacity) constructor allocates in advance buffer of size capacity  By default 16 characters are allocated  Capacity  Capacity holds the currently allocated space (in characters)  this[int index]  this[int index] (indexer in C#) gives access to the char value at given position  Length  Length holds the length of the string in the buffer 42

The StringBuilder Class (2)  sb.Append(…)  sb.Append(…) appends a string or another object after the last character in the buffer  sb.Remove(int startIndex, int length)  sb.Remove(int startIndex, int length) removes the characters in given range  sb.Insert(int index, string str)  sb.Insert(int index, string str) inserts given string (or object) at given position  sb.Replace(string oldStr, string newStr)  sb.Replace(string oldStr, string newStr) replaces all occurrences of a substring  sb.ToString() StringBuilder String  sb.ToString() converts the StringBuilder to String 43

44  Extracting all capital letters from a string StringBuilder – Another Example public static string ExtractCapitals(string s) { StringBuilder result = new StringBuilder(); StringBuilder result = new StringBuilder(); for (int i = 0; i < s.Length; i++) for (int i = 0; i < s.Length; i++) { if (char.IsUpper(s[i])) if (char.IsUpper(s[i])) { result.Append(s[i]); result.Append(s[i]); } } return result.ToString(); return result.ToString();}

Using StringBuilder Live Demo

Exercises in Class

Summary  Strings are immutable sequences of System.String characters (instances of System.String )  Can only be iterated  Support operations such as Substring(), IndexOf(), Trim(), etc.  Changes to the string create a new object, instead of modifying the old one  StringBuilder offers good performance  Recommended when concatenating strings in a loop 47

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License  This course (slides, examples, demos, videos, homework, etc.) is licensed under the "Creative Commons Attribution- NonCommercial-ShareAlike 4.0 International" licenseCreative Commons Attribution- NonCommercial-ShareAlike 4.0 International  Attribution: this work may contain portions from  "Fundamentals of Computer Programming with C#" book by Svetlin Nakov & Co. under CC-BY-SA licenseFundamentals of Computer Programming with C#CC-BY-SA  "C# Part I" course by Telerik Academy under CC-BY-NC-SA licenseC# Part ICC-BY-NC-SA  "C# Part II" course by Telerik Academy under CC-BY-NC-SA licenseC# Part IICC-BY-NC-SA 49

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