1. Processing and Manipulating Text
Strings and RegEx
Processing and Manipulating Text
SoftUni Team
Technical Trainers
Software University
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2. Table of Contents What is a String? Manipulating Strings
Comparing, Concatenating, Searching
Extracting Substrings, Splitting
Building and Modifying Strings
Why the + Operator is Slow?
Using the StringBuilder Class
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3. Table of Contents (2) Regular Expressions Regular Expressions in C#
Characters
Operators
Constructs
Regular Expressions in C#
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4. Questions
sli.do #Tech

5. What is a String?
Strings are represented by System.String objects in .NET Framework
String objects contain an immutable (read-only) sequence of characters
Before initializing, a string variable has null value

6. Comparing, Concatenating, Searching, Extracting Substrings, Splitting*
Manipulating Strings
Comparing, Concatenating, Searching, Extracting Substrings, Splitting
(c) 2007 National Academy for Software Development - All rights reserved. Unauthorized copying or re-distribution is strictly prohibited.*

7. Comparing Strings Several ways to compare two strings:
Dictionary-based string comparison
Case-insensitive
Case-sensitive
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);

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

9. Concatenating Strings
There are two ways to combine strings:
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"

10. Searching in Strings
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
string =
int firstIndex = // 5
int noIndex = .IndexOf("/"); // -1
string verse = "To be or not to be..";
int lastIndex = verse.LastIndexOf("be"); // 16

11. Problem: Count substring occurrences
You are given a text and a pattern
Find how many times that pattern is in the text.
Overlapping is allowed
ababa caba
aba
aaaaaa aa 3 5
Welcome to SoftUni
Java
Check your solution here:

12. Solution: Count substring occurrences
string input = Console.ReadLine().ToLower();
string pattern = Console.ReadLine().ToLower();
int counter = 0;
int index = input.IndexOf(pattern);
while (index != -1) {
counter++;
index = input.IndexOf(pattern, index + 1) }
Console.WriteLine(counter);

13. Extracting Substrings
str.Substring(int startIndex, int length)
str.Substring(int startIndex)
string filename
string name = filename.Substring(8, 8);
// name is Rila2005
string filename
string nameAndExtension = filename.Substring(8);
// nameAndExtension is Summer2009.jpg 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 C : \ P i c s R l a . j p g

14. 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); }

15. Other String Operations*
Other String Operations
Replacing Substrings, Deleting Substrings, Changing Character Casing, Trimming
(c) 2007 National Academy for Software Development - All rights reserved. Unauthorized copying or re-distribution is strictly prohibited.*

16. 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) – 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);
// $ 4567

17. Problem: Text filter You are given a text and a string of banned words
Replace all banned words in the text.
You should replace with "*", equal to the word's length
Linux, Windows
It is not Linux, it is GNU/Linux. Linux is merely the kernel, while GNU adds the functionality...
It is not *****, it is GNU/*****. ***** is merely the kernel, while GNU adds the functionality...
Check your solution here:

18. Contains(…) checks if string contains another string
Solution: Text Filter
string[] banWords = Console.ReadLine()
.Split(…); // ToDo: Add seprators
string text = Console.ReadLine();
foreach (var banWord in banWords) {
if (text.Contains(banWord))
text = text.Replace(banWord, new string('*', banWord.Length)); }
Console.WriteLine(text);
Contains(…) checks if string contains another string

19. Changing Character Casing
Using the method ToLower()
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);

20. Trimming White Space
str.Trim() – trims whitespaces at start and end of string
str.Trim(params char[] chars)
str.TrimStart() and str.TrimEnd()
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# ";

21. String Operations
Exercises in class

22. Building and Modifying Strings
Using the StringBuilder Class

23. StringBuilder: How It Works?
Capacity
StringBuilder:
Length = 9
Capacity = 15 H e l o , C # !
used buffer
(Length)
unused buffer
StringBuilder keeps a buffer memory, allocated in advance
Most operations use the buffer memory and do not allocate new objects

24. Changing the Contents of a String*
Changing the Contents of a String
Use the System.Text.StringBuilder class for modifiable strings of characters:
Use StringBuilder if you need to keep adding characters to a string
public static string ReverseString(string s) {
StringBuilder sb = new StringBuilder();
for (int i = s.Length - 1; i >= 0; i--)
sb.Append(s[i]); }
return sb.ToString();
Introducing the StringBuffer Class
StringBuffer represents strings that can be modified and extended at run time. The following example creates three new String objects, and copies all the characters each time a new String is created:
String quote = "Fasten your seatbelts, ";
quote = quote + "it's going to be a bumpy night.";
It is more efficient to preallocate the amount of space required using the StringBuffer constructor, and its append() method as follows:
StringBuffer quote = new StringBuffer(60); // allocate 60 chars
quote.append("Fasten your seatbelts, "); quote.append(" it's going to be a bumpy night. ");
StringBuffer also provides a number of overloaded insert() methods for inserting various types of data at a particular location in the string buffer.
Instructor Note
The example in the slide uses StringBuffer to reverse the characters in a string. A StringBuffer object is created, with the same length as the string. The loop traverses the String parameter in reverse order and appends each of its characters to the StringBuffer object by using append(). The StringBuffer therefore holds a reverse copy of the String parameter. At the end of the method, a new String object is created from the StringBuffer object, and this String is returned from the method.
(c) 2007 National Academy for Software Development - All rights reserved. Unauthorized copying or re-distribution is strictly prohibited.*

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

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

27. Demo: String concatenation
Given the code below try to optimize it to go under 10 secs.
Do not change the loop nor the Convert.ToString() method

28. Groups, Quantifiers, Anchors
Regular Expressions
Groups, Quantifiers, Anchors
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29. Character Classes [nvj] matches any character that is either n, v or j
[^abc] – matches any character that is not a, b or c
[0-9] - Character range: Мatches any digit frm 0 to 9
node.js v0.12.2
Abraham Lincoln
In 1519 Leonardo da Vinci died at the age of 67.

30. Character Classes (2)
\w – Matches any word character (a-z, A-Z, 0-9, _)
\W – Matches any non-word character (the opposite of \w)
\s – Matches any white-space character
\S – Matches any non-white-space character (opposite of \s)
\d – Matches any decimal digit
\D – Matches any non-decimal digit (opposite of \d)
aBcd 09_ &*^ Ю-Я
aBcd 09_ &*^ Ю-Я
\w – Matches any word character (a-z, A-Z, 0-9, _)
\W – Matches any non-word character (the opposite of \w)
\s – Matches any white-space character
\S – Matches any non-white-space character (opposite of \s)
\d – Matches any decimal digit
\D – Matches any non-digit character (opposite of \d)
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31. Quantifiers * - Matches the previous element zero or more times
+ - Matches the previous element one or more times
? - Matches the previous element zero or one time +
\+\d*
=> +
\+\d+
=>
\+\d?
=> +

32. Character Escapes
Sometimes you will need to look for special characters like new lines or tabulations
Then we have a new line
This is a “tab”
Name: Peter
Phone:
We can use character escapes in our RegEx like that:
Name:\t\w+\nPhone:\s*\+\d+

33. Anchors
^ - The match must start at the beginning of the string or line
$ - The match must occur at the end of the string
Example – username validation pattern:
Note: Test one by one, $ asserts string end
^\w{6,12}$
jeff_butt
short
johnny
too_long_username

34. Problem: Match full name
You are given a sequence of words
Find those who are full names
You can use RegXr or Regex101
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35. Grouping Constructs
(subexpression) - captures the matched subexpression and assigns it a number
(?:subexpression) – Defines a non-capturing group
\d{2}-(\w{3})-\d{4}
=>
22-Jan-2015
^(?:Hi|hello),\s*(\w+)$
=>
Hi, Peter

36. Backreference Constructs

37. Backreference Constructs
\number – matches the value of a numbered subexpression
\k<name> – matches the value of a named expression
05/08/2016
\d{2}(-|\/)\d{2}\1\d{4}
=>
05/08/2016
\d{2}(?<del>-|\/)\d{2}\k<del>\d{4}
=>

38. Playing with RegEx
Exercises in class

39. Using Built-In Regex Classes
Regular Expressions
Using Built-In Regex Classes

40. Regex C# supports a built-in regular expression class - Regex
Located in System.Text.RegularExpressions namespace
string pattern
Regex regex = new Regex(pattern);

41. Validating String By Pattern
IsMatch(string text) – determines whether the text matches the pattern
string text = "Today is ";
string pattern
Regex regex = new Regex(pattern);
bool containsValidDate = regex.IsMatch(text);
Console.WriteLine(containsValidDate); // True

42. Checking for a Single Match
Match(string text) – returns the first match that corresponds to the pattern
string text = "Nakov: 123";
string pattern (\d+)";
Regex regex = new Regex(pattern);
Match match = regex.Match(text);
Console.WriteLine(match.Groups.Count); // 3
Console.WriteLine("Matched text: \"{0}\"", match.Groups[0]);
Console.WriteLine("Name: {0}", match.Groups[1]); // Nakov
Console.WriteLine("Number: {0}", match.Groups[2]); // 123

43. Checking for Matches
Matches(string text) – returns a collection of matching strings that correspond to the pattern
string text = "Nakov: 123, Branson: 456";
string pattern (\d+)";
Regex regex = new Regex(pattern);
MatchCollection matches = regex.Matches(text, pattern);
Console.WriteLine("Found {0} matches", matches.Count);
foreach (Match match in matches) {
Console.WriteLine("Name: {0}", match.Groups[1]); }
// Found 2 matches
// Name: Nakov
// Name: Branson

44. Replacing With Regex
Replace(string text, string replacement) – replaces all strings that match the pattern with the provided replacement
string text = "Nakov: 123, Branson: 456";
string pattern
string replacement = "999";
Regex regex = new Regex(pattern);
string result = regex.Replace(text, replacement);
Console.WriteLine(result);
// Nakov: 999, Branson: 999

45. Problem: Replace <a> tag
You are given a html text.
Replace all <a> tags in it with [URL].
<ul> <li> <a href="
</li> </ul>
<ul> <li> [URL href="
</li></ul>
Check your solution here:

46. Solution: Replace <a> tag
string text = Console.ReadLine();
while (text != "end") {
string pattern =
@"<a.*?href.*?=(.*)>(.*?)<\/a>";
string replace href=$1]$2[/URL]";
string replaced = Regex.Replace(text, pattern,
replace);
Console.WriteLine(replaced);
text = Console.ReadLine(); }
You can try also: @"<a.*href=((?:.|\n)*?(?=>))>((?:.|\n)*?(?=<))<\/a>"
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47. Splitting With Regex
Split(string text) – splits the text by the pattern
Returns string[]
string text = " ";
string pattern
string[] results = Regex.Split(text, pattern);
Console.WriteLine(string.Join(", ", results)); // 1, 2, 3, 4

48. Built-in RegEx
Exercises in class

49. Summary Strings are immutable sequences of characters*
Summary
Strings are immutable sequences of
characters
Changes to the string create a new object,
instead of modifying the old one
StringBuilder offers good performance
Regular expressions describe patterns for
searching through text
Define special characters, operators and
constructs for building complex patterns
(c) 2007 National Academy for Software Development - All rights reserved. Unauthorized copying or re-distribution is strictly prohibited.*

50. Version control systems
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51. License
This course (slides, examples, demos, videos, homework, etc.) is licensed under the "Creative Commons Attribution- NonCommercial-ShareAlike 4.0 International" license
Attribution: this work may contain portions from
"Fundamentals of Computer Programming with C#" book by Svetlin Nakov & Co. under CC-BY-SA license
"C# Part I" course by Telerik Academy under CC-BY-NC-SA license
"C# Part II" course by Telerik Academy under CC-BY-NC-SA license
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52. Free Trainings @ Software University
Software University Foundation – softuni.org
Software University – High-Quality Education, Profession and Job for Software Developers
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Software Facebook
facebook.com/SoftwareUniversity
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youtube.com/SoftwareUniversity
Software University Forums – forum.softuni.bg
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