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CS 112 Introduction to
Programming
Lecture #21:
Strings and Characters
http://flint.cs.yale.edu/cs112/
Class String
r A string is essentially an encapsulation of an array of characters
m since we use string so often, C# defines the string class and
provides many methods (behaviors)
r We have already seen several methods
m method ToUpper
- replaces lower case letter
- original string remains unchanged
m method ToLower
- replaces lower case letter
- original string remains unchanged
m Method Format
r We will cover some methods; for many other methods, please
read chap. 6 of the textbook and the String method link on the
lecture-notes page
Class String: Creating New Strings
r Constructors
m C# provides eight constructors for initializing
strings
r CopyTo method
m copies specified number of characters into a char
array
r Substring method
m extracts a sub string
r Concat method
m Combine two strings
Outline
StringConstructo
r.cs
1 // StringConstructor.cs 2 // Demonstrating String class constructors. 3 4 using System; 5 using System.Windows.Forms; 6 7 // test several String class constructors 8 class StringConstructor 9 { 10 // The main entry point for the application. 11 [STAThread] 12 static void Main( string[] args ) 13 { 14 string output; 15 string originalString, string1, string2, 16 string3, string4; 17 18 char[] characterArray = 19 { 'b', 'i', 'r', 't', 'h', ' ', 'd', 'a', 'y' }; 20 21 // string initialization 22 originalString = "Welcome to C# programming!"; 23 string1 = originalString; 24 string2 = new string( characterArray ); 25 string3 = new string( characterArray, 6, 3 ); 26 string4 = new string( 'C', 5 ); 27 28 output = "string1 = " + """ + string1 + ""\n" + 29 "string2 = " + """ + string2 + ""\n" + 30 "string3 = " + """ + string3 + ""\n" + 31 "string4 = " + """ + string4 + ""\n"; 32
String constructor takes a
character array as argument
String constructor takes a char
array and two int arguments
Starting index and count
Using string constructed with a character
and an int specifying number of times to
repeat character in the string
Outline
StringConstructo
r.cs
Program Output
33 MessageBox.Show( output, "String Class Constructors", 34 MessageBoxButtons.OK, MessageBoxIcon.Information ); 35 36 } // end method Main 37 38 } // end class StringConstructor
Shows the output
Outline
StringMethods.cs
1 // StringMethods.cs 2 // Using the indexer, property Length and method CopyTo 3 // of class String. 4 5 using System; 6 using System.Windows.Forms; 7 8 // creates string objects and displays results of using 9 // indexer and methods Length and CopyTo 10 class StringMethods 11 { 12 // The main entry point for the application. 13 [STAThread] 14 static void Main( string[] args ) 15 { 16 string string1, output; 17 char[] characterArray; 18 19 string1 = "hello there"; 20 characterArray = new char[ 5 ]; 21 22 // output string 23 output = 24 "string1: "" + string1 + """; 25 26 // test Length property 27 output += "\nLength of string1: " + string1.Length; 28 29 // loop through character in string1 and display 30 // reversed 31 output += "\nThe string reversed is: "; 32 33 for ( int i = string1.Length - 1; i >= 0; i-- ) 34 output += string1[ i ]; 35
String declarations
String1 to store string
literal “hello there”
Append to output of
string1 in reverse order
Outline
StringMethods.cs
Program Output
36 // copy characters from string1 into characterArray 37 string1.CopyTo( 0, characterArray, 0, 5 ); 38 output += "\nThe character array is: "; 39 40 for ( int i = 0 ; i < characterArray.Length; i++ ) 41 output += characterArray[ i ]; 42 43 MessageBox.Show( output, "Demonstrating the string " + 44 "Indexer, Length Property and CopyTo method", 45 MessageBoxButtons.OK, MessageBoxIcon.Information ); 46 47 } // end method Main 48 49 } // end class StringMethods
Index to begin copying
character array to copy to
Index of location to put
into character array
Number of characters
to copy from string
Method Copyto called by string
Outline
SubString.cs
1 // SubString.cs 2 // Demonstrating the String Substring method. 3 4 using System; 5 using System.Windows.Forms; 6 7 // creating substrings 8 class SubString 9 { 10 // The main entry point for the application. 11 [STAThread] 12 static void Main( string[] args ) 13 { 14 string letters = "abcdefghijklmabcdefghijklm"; 15 string output = ""; 16 17 // invoke Substring method and pass it one parameter 18 output += "Substring from index 20 to end is "" + 19 letters.Substring( 20 ) + ""\n"; 20 21 // invoke Substring method and pass it two parameters 22 output += "Substring from index 0 to 6 is "" + 23 letters.Substring( 0, 6 ) + """; 24 25 MessageBox.Show( output, 26 "Demonstrating String method Substring", 27 MessageBoxButtons.OK, MessageBoxIcon.Information ); 28 29 } // end method Main 30 31 } // end class SubString
First argument specify
the starting index
Second argument specify
length of the substring to be
copied
Outline
SubString.cs
Program Output
Outline
SubConcatination
.cs
1 // SubConcatination.cs 2 // Demonstrating String class Concat method. 3 4 using System; 5 using System.Windows.Forms; 6 7 // concatenates strings using String method Concat 8 class StringConcatenation 9 { 10 // The main entry point for the application. 11 [STAThread] 12 static void Main( string[] args ) 13 { 14 string string1 = "Happy "; 15 string string2 = "Birthday"; 16 string output; 17 18 output = "string1 = "" + string1 + ""\n" + 19 "string2 = "" + string2 + """; 20 21 output += 22 "\n\nResult of String.Concat( string1, string2 ) = " + 23 String.Concat( string1, string2 ); 24 25 output += "\nstring1 after concatenation = " + string1; 26 27 MessageBox.Show( output, 28 "Demonstrating String method Concat", 29 MessageBoxButtons.OK, MessageBoxIcon.Information ); 30 31 } // end method Main 32 33 } // end class StringConcatenation
Declare two new string s
Append string2 unto
the end of string
The original string , string
is not altered
Output the result from the
ConCat method call
Outline
SubConcatination
.cs
Program Output
Class String: Comparison and string Search
r Comparison
m Methods CompareTo and Equals
- uses lexicographical comparison
m Methods StartsWith and EndsWith
r Find the position of a char or string
m IndexOf
m IndexOfAny
m LastIndexOf
m LastIndexOfAny
Outline
StringIndexMetho
ds.cs
35 output += "\nLast '$' is located at index " + 36 letters.LastIndexOf( '$', 15, 5 ); 37 38 // test IndexOf to locate a substring in a string 39 output += "\n\n"def" is located at" + 40 " index " + letters.IndexOf( "def" ); 41 42 output += "\n"def" is located at index " + 43 letters.IndexOf( "def", 7 ); 44 45 output += "\n"hello" is located at index " + 46 letters.IndexOf( "hello", 5, 15 ); 47 48 // test LastIndexOf to find a substring in a string 49 output += "\n\nLast "def" is located at index " + 50 letters.LastIndexOf( "def" ); 51 52 output += "\nLast "def" is located at " + 53 letters.LastIndexOf( "def", 25 ); 54 55 output += "\nLast "hello" is located at index " + 56 letters.LastIndexOf( "hello", 20, 15 ); 57 58 // test IndexOfAny to find first occurrence of character 59 // in array 60 output += "\n\nFirst occurrence of 'c', 'a', '$' is " + 61 "located at " + letters.IndexOfAny( searchLetters ); 62 63 output += "\nFirst occurrence of 'c, 'a' or '$' is " + 64 "located at " + letters.IndexOfAny( searchLetters, 7 ); 65 66 output += "\nFirst occurrence of 'c', 'a' or '$' is " + 67 "located at " + letters.IndexOfAny( searchLetters, 20, 5 ); 68
Instead of sending character
arguments, these two methods
search substring argument
Method IndexOfAny take
an array of characters as
the first argument; returns
the index of first
occurrence of any
characters specified in the
character array argument
Outline
StringIndexMetho
ds.cs
69 // test LastIndexOfAny to find last occurrence of character 70 // in array 71 output += "\n\nLast occurrence of 'c', 'a' or '$' is " + 72 "located at " + letters.LastIndexOfAny( searchLetters ); 73 74 output += "\nLast occurrence of 'c', 'a' or '$' is " + 75 "located at " + letters.LastIndexOfAny( searchLetters, 1 ); 76 77 output += "\nLast occurrence of 'c', 'a' or '$' is " + 78 "located at " + letters.LastIndexOfAny( 79 searchLetters, 25, 5 ); 80 81 MessageBox.Show( output, 82 "Demonstrating class index methods", 83 MessageBoxButtons.OK, MessageBoxIcon.Information ); 84 85 } // end method Main 86 87 } // end class StringIndexMethods
Outline
StringIndexMetho
ds.cs
Program Output
More String Methods
r Method Trim
m removes whitespaces at the beginning and
end
m original string is changed
r Method Replace
m Change all occurrences of one char or string with
another one
m original string remains unchanged
Outline
StringMiscellane
ous2.cs
1 // StringMethod2.cs 2 // Demonstrating String methods Replace, ToLower, ToUpper, Trim 3 // and ToString. 4 5 using System; 6 using System.Windows.Forms; 7 8 // creates strings using methods Replace, ToLower, ToUpper, Trim 9 class StringMethods 10 { 11 // The main entry point for the application. 12 [STAThread] 13 static void Main( string[] args ) 14 { 15 string string1 = "cheers!"; 16 string string2 = "GOOD BYE "; 17 string string3 = " spaces "; 18 string output; 19 20 output = "string1 = "" + string1 + ""\n" + 21 "string2 = "" + string2 + ""\n" + 22 "string3 = "" + string3 + """; 23 24 // call method Replace 25 output += 26 "\n\nReplacing "e" with "E" in string1: "" + 27 string1.Replace( 'e', 'E' ) + """; 28 29 // call ToLower and ToUpper 30 output += "\n\nstring1.ToUpper() = "" + 31 string1.ToUpper() + ""\nstring2.ToLower() = "" + 32 string2.ToLower() + """; 33
Method Replace return new
string with correct revision
based on the argument
Replace all instances of
‘e’ with ‘E’ in string
String to search for String to replace with
Outline
StringMiscellane
ous2.cs
Program Output
34 // call Trim method 35 output += "\n\nstring3 after trim = "" + 36 string3.Trim() + """; 37 38 // call ToString method 39 output += "\n\nstring1 = "" + string1 + """; 40 41 MessageBox.Show( output, 42 "Demonstrating various string methods", 43 MessageBoxButtons.OK, MessageBoxIcon.Information ); 44 45 } // end method Main 46 47 } // end class StringMethods
Method Trim to remove all
whitespace character at the
beginning or end of string3;
Return new string omitting
leading or trailing
whitespace character
Backup Slides
Class StringBuilder
r Class StringBuilder
m Create and manipulate dynamic string information
m Capable of resizing
Outline
StringBuilderCon
structor.cs
1 // StringBuilderConstructor.cs 2 // Demonstrating StringBuilder class constructors. 3 4 using System; 5 using System.Windows.Forms; 6 using System.Text; 7 8 // creates three StringBuilder with three constructors 9 class StringBuilderConstructor 10 { 11 // The main entry point for the application. 12 [STAThread] 13 static void Main( string[] args ) 14 { 15 StringBuilder buffer1, buffer2, buffer3; 16 string output; 17 18 buffer1 = new StringBuilder(); 19 buffer2 = new StringBuilder( 10 ); 20 buffer3 = new StringBuilder( "hello" ); 21 22 output = "buffer1 = "" + buffer1.ToString() + ""\n"; 23 24 output += "buffer2 = "" + buffer2.ToString() + ""\n"; 25 26 output += "buffer3 = "" + buffer3.ToString() + ""\n"; 27 28 MessageBox.Show( output, 29 "Demonstrating StringBuilder class constructors", 30 MessageBoxButtons.OK, MessageBoxIcon.Information ); 31 32 } // end method Main 33 34 } // end class StringBuilderConstructor
No-argument StringBuilder
constructor with default initial
capacity at 16
Initial capacity is the smallest
power of two greater than the
number of characters in the
string argument
Method ToString to obtain
string representation of the
StringBuilders’ content;
Method returns the
StringBuilders’ underlying
string
Outline
StringBuilderCon
structor.cs
Program Output
StringBuilder Indexer, Length and Capacity
Properties, and EnsureCapacity Method
r Method EnsureCapacity
m Allows programmers to guarantee StringBuilder
has capacity that reduces the number of times
capacity must be increased
m Doubles StringBuiler instance’s current
capacity
m Length property returns number of character in
StringBuilder
m Capacity property returns number
StringBuilder can store without allocating
memory
Outline
StringBuilderFea
tures.cs
1 // StringBuilderFeatures.cs 2 // Demonstrating some features of class StringBuilder. 3 4 using System; 5 using System.Windows.Forms; 6 using System.Text; 7 8 // uses some of class StringBuilder’s methods 9 class StringBuilderFeatures 10 { 11 // The main entry point for the application. 12 [STAThread] 13 static void Main( string[] args ) 14 { 15 StringBuilder buffer = 16 new StringBuilder( "Hello, how are you?" ); 17 18 // use Length and Capacity properties 19 string output = "buffer = " + buffer.ToString() + 20 "\nLength = " + buffer.Length + 21 "\nCapacity = " + buffer.Capacity; 22 23 // use EnsureCapacity method 24 buffer.EnsureCapacity( 75 ); 25 26 output += "\n\nNew capacity = " + 27 buffer.Capacity; 28 29 // truncate StringBuilder by setting Length property 30 buffer.Length = 10; 31 32 output += "\n\nNew length = " + 33 buffer.Length + "\nbuffer = "; 34
Declare a StringBuilder
name buffer
Take string argument
to initialize its value
to the actual string
Append to output the
length of StringBuilder
Append to output the
capacity of StringBuilder
Expands the capacity to a
minimum of 75 characters
Uses Length ’s Set accessor to set
length of the Stringbuilder to 10
StringBuilder Insert, Remove and
Replace Methods
r Insert method
m StringBuilder provides 18 overloaded methods
• Insert into at any position
m Program may throw
ArgumentOutOfRangeException
r Remove method
m Takes two argument
m Program may throw
ArgumentOutOfRangeException
r Replace method
m Substitute specified string
Outline
StringBuilderIns
ertRemove.cs
1 // StringBuilderInsertRemove.cs 2 // Demonstrating methods Insert and Remove of the 3 // StringBuilder class. 4 5 using System; 6 using System.Windows.Forms; 7 using System.Text; 8 9 // test the Insert and Remove methods 10 class StringBuilderInsertRemove 11 { 12 // The main entry point for the application. 13 [STAThread] 14 static void Main( string[] args ) 15 { 16 object objectValue = "hello"; 17 string stringValue = "good bye"; 18 char[] characterArray = { 'a', 'b', 'c', 19 'd', 'e', 'f' }; 20 21 bool booleanValue = true; 22 char characterValue = 'K'; 23 int integerValue = 7; 24 long longValue = 10000000; 25 float floatValue = 2.5F; 26 double doubleValue = 33.333; 27 StringBuilder buffer = new StringBuilder(); 28 string output; 29 30 // insert values into buffer 31 buffer.Insert(0, objectValue); 32 buffer.Insert(0, " "); 33 buffer.Insert(0, stringValue); 34 buffer.Insert(0, " ");
Various different
type of objects
created to append
Uses the Insert method
Outline
StringBuilderIns
ertRemove.cs
35 buffer.Insert(0, characterArray); 36 buffer.Insert(0, " "); 37 buffer.Insert(0, booleanValue); 38 buffer.Insert(0, " "); 39 buffer.Insert(0, characterValue); 40 buffer.Insert(0, " "); 41 buffer.Insert(0, integerValue); 42 buffer.Insert(0, " "); 43 buffer.Insert(0, longValue); 44 buffer.Insert(0, " "); 45 buffer.Insert(0, floatValue); 46 buffer.Insert(0, " "); 47 buffer.Insert(0, doubleValue); 48 buffer.Insert(0, " "); 49 50 output = "buffer after inserts: \n" + 51 buffer.ToString() + "\n\n"; 52 53 buffer.Remove( 10, 1 ); // delete 2 in 2. 54 buffer.Remove( 2, 4 ); // delete .333 in 33. 55 56 output += "buffer after Removes:\n" + 57 buffer.ToString(); 58 59 MessageBox.Show( output, "Demonstrating StringBuilder " + 60 "Insert and Remove methods", MessageBoxButtons.OK, 61 MessageBoxIcon.Information ); 62 63 } // end method Main 64 65 } // end class StringBuilderInsertRemove
Outline
StringBuilderIns
ertRemove.cs
Program Output
Changes to the
string from the
Remove method call
Outline
StringBuilderRep
lace.cs
1 // StringBuilderReplace.cs 2 // Demonstrating method Replace. 3 4 using System; 5 using System.Windows.Forms; 6 using System.Text; 7 8 // testing the Replace method 9 class StringBuilderReplace 10 { 11 // The main entry point for the application. 12 [STAThread] 13 static void Main( string[] args ) 14 { 15 StringBuilder builder1 = 16 new StringBuilder( "Happy Birthday Jane" ); 17 18 StringBuilder builder2 = 19 new StringBuilder( "good bye greg" ); 20 21 string output = "Before replacements:\n" + 22 builder1.ToString() + "\n" + builder2.ToString(); 23 24 builder1.Replace( "Jane", "Greg" ); 25 builder2.Replace( 'g', 'G', 0, 5 ); 26 27 output += "\n\nAfter replacements:\n" + 28 builder1.ToString() + "\n" + builder2.ToString(); 29
StringBuilder created
with specified string s
Replace “Jane” with “Greg”
Replaces all instances of the
first character with the second
Index specify begin point
and continuation span
Outline
StringBuilderRep
lace.cs
Program Output
30 MessageBox.Show( output, 31 "Using StringBuilder method Replace", 32 MessageBoxButtons.OK, MessageBoxIcon.Information ); 33 34 } // end method Main 35 36 } // end class StringBuilderReplace
Result from replacing “Jane” with
“Greg”
The continuation span of five was
insufficient for “greg” to be altered
