Strings
Telerik Academy Alpha

 

 Table of contents

What are strings?

 What are strings?

  • string is a data type

    • System.String class

  • Sequence of characters (Unicode symbols)

0 1 2 3 4
H e l l o
0x12345 0x12346 0x12347 0x12348 0x12349
Index
Variable
Address
string text = "Hello";

 What are strings?

  • In the namespace System there is a class String which represents the string in C#​

    • Strings use Unicode to support multiple languages and alphabets

 Immutable

  • String objects are immutable: they cannot be changed after they have been created.

  • All the methods and operators actually return new object

string text = "Hello, Telerik Academy";
Console.WriteLine(text[0]);
		
// Compilation error indexer 'string.this[int]' 
// cannot be assigned to -- it is read only
text[0] = 'A';

 Immutable

string text = "Hello";

// This is a completely new object
text += ", Telerik Academy!";

Console.WriteLine(text); // Hello, Telerik Academy!

 Immutable - Demo

 Strings are arrays?

  • String objects have similarities to arrays but they are NOT arrays

    • It is like array of characters

    • Fixed Length ( str.Length)

    • Indexers ( str[0], str[1], ... str[str.Length-1] )

    • You can iterate them with for and foreach loops 

String operations

Compare

 Compare

string text = "Telerik Academy";
string text1 = "telerik academy";

Console.WriteLine(text == text1); // False

  • Equality compare with == operator

    • case-sensitive comparison

string text = "Telerik Academy";
string text1 = "Telerik Academy";

Console.WriteLine(text == text1); // True

 Compare

  • Equality compare with Equals() method

    • the same as == in C# (ex: in Java this is not true)

    • you can control if it is case-sensitive/insensitive

      • with the second parameter StringComparison enum

string a = "Telerik Academy";
string a1 = "telerik academy";

// False
Console.WriteLine(a.Equals(a1)); 
// True
Console.WriteLine(a.Equals(a1, StringComparison.CurrentCultureIgnoreCase));

Concatenate

 Concatenate

  • Concatenation of strings could be done with +/+= operators

string text = "Telerik Academy";
string text1 = "Alpha";

string newText = text + " " + text1;

 Concatenate

  • Or with Concat() method

string text = "Telerik Academy";
string text1 = "Alpha";

string space = " ";

string newText = string.Concat(text, space, text1, space, "Rocks!");
// Telerik Academy Alpha Rocks!

Search in strings

 Search

  • When you need to find a character in a string

    • IndexOf() method

      • returns the position of the element

      • or negative number if not found

      • case-sensitive but could be changed

string text = "Telerik Academy";
Console.WriteLine(text.IndexOf('T')); // 0
Console.WriteLine(text.IndexOf('t')); // -1

 Search

  • IndexOf() has many useful overloads

    • with different parameters

      • startIndex, count comparisonType, etc.

string text = "Telerik Academy";

text.IndexOf('t'); // -1
text.IndexOf("te", StringComparison.CurrentCultureIgnoreCase); // 0

 Search

  • In addition to IndexOf() there are other useful methods for searching

    • LastIndexOf()

    • IndexOfAny()

    • LastIndexOfAny()

string text = "Telerik Academy";

Console.WriteLine(text.IndexOf('e')); // 1
Console.WriteLine(text.LastIndexOf('e')); // 12

Extract parts

 Extract

  • You can get part of the string with optional start and end position

string text = "Telerik Academy";

Console.WriteLine(text.Substring(8)); // Academy
Console.WriteLine(text.Substring(0, 7)); // Telerik

 Extract delimited

  • You can all the parts of the string as array by delimiter (",", ".", " " or any symbol you need)

string text = "Telerik Academy";

string[] arr = text.Split(' ');

Console.WriteLine(arr.Length); // 2

 Extract delimited

  • There could be empty string when splitting

string text = "Telerik Academy ";

// ["Telerik", "Academy", ""] empty string at the end
string[] arr = text.Split(' ');

Console.WriteLine(arr.Length); // 3

 Extract delimited

  • How to handle empty strings (StringSplitOptions.RemoveEmptyEntries)

string text = "Telerik Academy ";

// you should pass array of chars or strings
var splitSymbols = new char[] { ' ', ',' };

// ["Telerik", "Academy"]
string[] arr = text.Split(splitSymbols, StringSplitOptions.RemoveEmptyEntries);

Console.WriteLine(arr.Length); // 2

Replace and remove

 Replace

  • You can replace all occurrences of a char/string in another string with new value

    • Replace() method

string text = "Telerik Academy";

// Replace returns new string (strings are immutable)
var newString = text.Replace("Telerik", "Alpha");

Console.WriteLine(newString); // Alpha Academy

 Remove/Delete

  • You can remove part of a string

    • Remove() method

      • startIndex

      • count (optional)

string text = "Telerik Academy";

// Remove returns new string (strings are immutable)
var newString = text.Remove(0, 8);

Console.WriteLine(newString); // Academy

Casing, trimming

 Casing

  • You can change character casing 

    • ToUpper()

    • ToLower()

    • etc.

string text = "Telerik Academy";

// ToUpper returns new string (strings are immutable)
var newString = text.ToUpper();

Console.WriteLine(newString); // TELERIK ACADEMY

 Trim

  • You can trim the string (any character) from start/end  

    • Trim() - trims start and end from whitespace

    • TrimEnd()  - only the end

    • TrimStart() - only the start

      • all the methods could contain different symbols to trim

string text = " Telerik Academy!";

// The methods could be chained
var newString = text.Trim().TrimEnd('!');

Console.WriteLine(newString);

 Demo

StringBuilder

Mutate the string

 StringBuilder

  • Performing multiple concatenations (ex: in for loop) is a slow operation due to the immutability if the strings

    • Every time you add a string to an existing one, there is a new object created and all the previous values are copied in it

    • It is slow if you want to add multiple times or build a long string 

      • If you just make a single concatenation it is okay to use simple string concatenation

 StringBuilder

StringBuilder sBuilder = new StringBuilder();

sBuilder.Append("Telerik");

            sBuilder.Append(" Academy");
T e l e r i k A c
a d e m y

 StringBuilder

  • StringBuilder uses internal array and this makes it faster

    • In the new versions of .NET (>= 4.0) StringBuilder uses Linked List of StringBuilder instances

    • Adding is much faster

  • If you need to add many strings or build a large string (ex: in a for loop) you must use StringBuilder

 StringBuilder

int count = 10000;
string str = string.Empty;
StringBuilder strBuilder = new StringBuilder();
Stopwatch sw = Stopwatch.StartNew();

for (int i = 0; i < count; i++)
{
    str += i;
}
Console.WriteLine($"String concatenate: {sw.ElapsedMilliseconds}"); // ~ 12500 ms
sw.Start();

for (int i = 0; i < count; i++)
{
    strBuilder.Append(i);
}
Console.WriteLine($"StringBuilder append: {sw.ElapsedMilliseconds}"); // ~ 10 ms

Summary

 String summary

  • Strings are immutable

    • Cannot be rewritten 

  • All the operations over strings return new string (object)

    • Therefore they are relatively slow

  • All the objects in C# have ToString() method

  • If you need to add many chars/strings and make multiple such operations 

    • Consider using StringBuilder

 Resources

Questions?

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