programs on string and string builder

String and StringBuilder


3.1 String Class

The most importent built-in class is the string class. The string class and the

StringBuilder class provide ways to perform string manipulations. The string

class provides an immutable object

string s = "Hello";

which means that once the value of the string instance is set, it cannot be changed.

Even though it appears that the application is changing the value of the string

instance, it is actually returning a new instance of the string class in memory.

// mystring.cs

using System;

class mystring

{

public static void Main()

{

string s1 = "otto";

int length = s1.Length;

Console.WriteLine(s1); // => otto

Console.WriteLine(length); // => 4

string s2 = "willi";

s2 = s2.Replace(’l’,’t’);

Console.WriteLine(s2); // witti

string s3 = "Johannesburg";

string result = s3.Substring(3,5);

Console.WriteLine(result); // => annes

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44 CHAPTER 3. STRING AND STRINGBUILDER

string s4 = "olli&ulli&ruedi";

string[] textarray = s4.Split(’&’);

Console.WriteLine(textarray[1]); // => ulli

string s5 = string.Join(":",textarray);

Console.WriteLine(s5); // => olli:ulli:ruedi

char[] s6 = { ’o’, ’p’, ’a’ };

string s7 = new string(s6);

Console.WriteLine(s7); // => opa

string s8 = "xeNa";

string s9 = s8.ToUpper();

Console.WriteLine(s9); // => XENA

string s10 = "WILLI HANS";

string s11 = s10.ToLower();

Console.WriteLine("s11 = " + s11); // => willi hans

// use + to concatenate strings

string s12 = "Carl-";

string s13 = "Otto";

string s14 = s12 + s13;

Console.WriteLine("s14 = " + s14);

// use Equals() to compare strings

// case sensitive

bool b1 = s12.Equals(s13);

Console.WriteLine("b1 = " + b1); // => False

// can also use overloaded == to compare strings

// case sensitive

bool b2 = (s12 == s13);

Console.WriteLine("b2 = " + b2); // => False

// copy a string

string s15 = string.Copy(s14);

Console.WriteLine("s15 = " + s15);

} // end Main

}

Arrays of strings can be implemented as follows.

// stringarrays.cs

3.2. CONVERT CLASS 45

using System;

class stringarrays

{

public static void Main()

{

// one-dimensional array of strings

string[] keywords = new string[] { "as", "do", "if", "in" };

Console.WriteLine(keywords[3]); // => in

// one-dimensional array of strings

string[] names = { "willi", "ola", "xena" };

Console.WriteLine(names[2]); // => xena

// two-dimensional array of strings

string[,] strArry = {{"1","one"}, {"2","two"}, {"3","three"}};

Console.WriteLine(strArry[0,0]); // => 1

Console.WriteLine(strArry[2,0]); // => 3

} // end Main

}

3.2 Convert Class

Using the Convert class we can convert string to numbers (integers and floating

point) and numbers (integers and floating point) to strings. The methods are

string ToString(T x) // any numerical type

bool ToBoolean(string s)

byte ToByte(string s)

char ToChar(string s)

short ToInt16(string s)

int ToInt32(string s)

long ToInt64(string s)

float ToSingle(string s)

double ToDouble(string s)

decimal ToDecimal(string s)

An example is

// MyConvert.cs

using System;

public class MyConvert

46 CHAPTER 3. STRING AND STRINGBUILDER

{

public static void Main()

{

int i = 34;

string s1 = Convert.ToString(i);

Console.WriteLine("s1 = " + s1);

double x = 3.14159;

string s2 = Convert.ToString(x);

Console.WriteLine("s2 = " + s2);

bool b = Convert.ToBoolean("true");

Console.WriteLine("b = " + b);

char c = Convert.ToChar("x");

Console.WriteLine("c = " + c);

int j = Convert.ToInt32("12345");

Console.WriteLine("j = " + j);

string s3 = "3.14159";

double y = Convert.ToDouble(s3);

Console.WriteLine("y = " + y);

}

}

3.3 StringBuilder Class

The StringBuilder class represents a mutable string a characters. It is called mutable

because it can be modified once it has been created by using the methods

Append(), Insert(), Remove() and Replace(). The StringBuilder class is defined

in the System.Text namespace. Thus we have to add the following line in our

application.

using System.Text;

Using the StringBuilder class.

// mystringbuilder.cs

using System;

using System.Text; // for StringBuilder

class mystringbuilder

{

public static void Main()

{

string s = "carl";

StringBuilder b1 = new StringBuilder(s.Length+12);

3.3. STRINGBUILDER CLASS 47

b1.Append("carl");

b1.Append("-uli");

Console.WriteLine(b1); // => carl-uli

b1.Remove(3,2);

Console.WriteLine(b1); // => caruli

StringBuilder b2 = new StringBuilder("A.C");

b2.Insert(2,"B.");

Console.WriteLine(b2); // => A.B.C

b2.Replace(’.’,’:’);

Console.WriteLine(b2); // => A:B:C

StringBuilder b3 = new StringBuilder("stringbuilder");

b3.Remove(4,9);

Console.WriteLine(b3); // => stri

}

}

Another application of the StringBuilder class is given by generating the Thue-

Morse sequence. We apply recursion, i.e. the method mythuemorse calls itself.

// thuemorse.cs

using System;

using System.Text;

class ThueMorse

{

public static void Main()

{

for(int i=0;i<7;i++)

Console.WriteLine(mythuemorse(i));

}

public static StringBuilder mythuemorse(int n)

{

if(n==0) return new StringBuilder("0",50);

StringBuilder tm = mythuemorse(n-1);

StringBuilder tm2 = new StringBuilder("",30);

for(int i=0;i

if(tm[i] == ’0’) tm2.Append("01"); else tm2.Append("10");

return tm2;

}

}