MANIPULATING STRINGS

Strings

The String  classes provide strings functionality in .NET. 

 Understanding the String Class

The String class implements the functionality of string data type. String class is defined in the System namespace. Here are few important things about the String class before we proceed:

1. An instance of String is immutable, means once an instance is created, it cannot be modified. There are methods, which returns a new String to return a new sub string from it.
2. Index of String is zero based. Means the first character of the index is 0th element of the String and last character of the String is total number of elements in the string - 1.
3. By default a String is an empty string (""). So you don't have to initialize it as you used to do in C++ or other languages. An empty string is greater than the null value.

String class Members

String class provides two properties - Chars and Length. The Chars property returns the character at a specified position in a string and the Length property returns the number of characters in a string.

String class provides two types of methods - static and instance. Static methods can only be used by String class, not by an instance of the String class. The instance methods are used by instances of the String class.

Static Methods of String/string

Compare: Compares the values of two strings.

Concat: Concatenates (joins) two or more strings into one string.

Copy: Creates a new string from an existing string.

Equals :Compares two strings to determine whether they contain the same value. Returns true if the two values are equal; otherwise, returns false.

Join :Concatenates two or more strings. A specified “separator string” is placed between each of the original strings.

Methods and Properties of Each Instance

Clone: Returns a copy of the stored string.

CompareTo: Compares the value of this string with the value of another string. Returns a negative number if this string is less than the compared string, 0 if equal, and a positive number if the value of this string is greater.

CopyTo: Copies a portion of or all of a string to a new string or character array.

EndsWith: Determines whether the end of the value stored in the string is equal to a

string value. If they are equal, true is returned; otherwise, false is returned.

Equals Compares two strings to determine whether they contain the same value.

Returns true if the two values are equal; otherwise, returns false.

IndexOf: Returns the index (location) of the first match for a character or string. Returns

-1 if the value is not found.

Insert :Inserts a value into a string. This is done by returning a new string.

LastIndexOf: Returns the index (location) of the last match for a character or a string.

Returns -1 if the value is not found.

Length: Returns the length of the value stored in the string. The length is equal to the

number of characters contained.

PadLeft: Right-justifies the value of a string and then pads any remaining spaces with a

specified character (or space).

PadRight: Left-justifies the value of a string and then pads any remaining spaces with a

specified character (or space).

Remove: Deletes a specified number of characters from a specified location within a

string.

Split: The opposite of Join. Breaks a string into substrings based on a specified value. The specified value is used as a breaking point.

StartsWith: Determines whether the value stored in a string starts with a specified character

or set of characters. Returns true if there is a match and false if not. If

specified character is null, true is also returned.

Substring: Returns a substring from the original string starting at a specified location. The

number of characters for the substring might also be specified but is not required.

ToCharArray: Copies the characters in the current string value to a char array.

ToLower: Returns a copy of the current value in all lowercase letters.

ToUpper: Returns a copy of the current value in all uppercase characters.

Trim: Removes copies of a specified string from the beginning and end of the current

string.

TrimEnd: Removes copies of a specified string from the end of the current string.

TrimStart: Removes copies of a specified string from the beginning of the current string.

Comparing Strings

The Compare method compares two strings and returns an integer value. The return value of Compare method can be less than zero, greater than zero or equals to zero

 The following code compares two strings and return results on the System console.

// Comparing two strings
//====================================
string str1 = "ppp";
string str2 = "ccc";
int res = String.Compare(str1, str2);
Console.WriteLine("First result:" +res.ToString());
str2 = "ttt"; res = String.Compare(str1, str2);
Console.WriteLine("Second result:" +res.ToString());
str1 = "ttt"; res = String.Compare(str1, str2);
Console.WriteLine("Third result:" +res.ToString));
//====================================

The CompareTo method is an instance method. It compares a value (either a string or on object) with a string instance. Return values of this method are same as the Compare method. The following source code compares two strings.

// CompareTo Method
string str = "kkk";
Console.WriteLine( str.CompareTo(str1) );

Copy and Concatenating Strings

The Concat method adds strings (or objects) and returns a new string. Using Concat method, you can add two strings, two objects and one string and one object or more combinations of these two.

The following source code concatenate two strings.

string str1 = "ppp";
string str2 = "ccc";
string strRes = String.Concat(str1, str2);
Console.WriteLine(strRes);

The following source code concatenates one string and one object.

object obj = (object)12;
strRes = String.Concat(str1, obj);
Console.WriteLine(strRes);

The Copy method copies contents of a string to another. The Copy method takes a string as input and returns another string with the same contents as the input string. For example, the following code copies str1 to strRes.

string str1 = "ppp";
string str2 = "ccc";
string strRes = String.Copy(str1);
Console.WriteLine("Copy result :" + strRes);

The CopyTo method copies a specified number of characters from a specified position in this instance to a specified position in an array of characters. For example, the following example copies contents of str1 to an array of characters. You can also specify the starting character of a string and number of characters you want to copy to the array.

string str1 = "ppp";
char[] chrs = new Char[2];
str1.CopyTo(0, chrs, 0, 2);

The Clone method returns a new copy of a string in form of object. The following code creates a clone of str1.

string str1 = "ppp";
object objClone = str1.Clone();
Console.WriteLine("Clone :"+objClone.ToString());

The Join method is useful when you need to insert a separator (String) between each element of a string array, yielding a single concatenated string. For example, the following sample inserts a comma and space (", ") between each element of an array of strings.

string str1 = "ppp";
string str2 = "ccc";
string str3 = "kkk";
string[] allStr = new String[]{str1, str2, str3};
string strRes = String.Join(", ", allStr);
Console.WriteLine("Join Results: "+ strRes);

Adding, Removing and Replacing Strings

The Insert method inserts a specified string at a specified index position in an instance. For example, the following source code inserts "bbb" after second character in str1 and the result string is "pbbbpp".

string str1 = "ppp";
string strRes = str1.Insert(2, "bbb");
Console.WriteLine(strRes.ToString());

The Remove method deletes a specified number of characters from a specified position in a string. This method returns result as a string. For example, the following code removes three characters from index 3.

string s = "123abc000";
Console.WriteLine(s.Remove(3, 3));

The Replace method replaces all occurrences of a specified character in a string. For example, the following source code replaces all p character instances of str1 with character l and returns string "lll".

string str1 = "ppp";
string repStr = str1.Replace('p', 'l');
Console.WriteLine("Replaced string:"+ repStr.ToString() );

The Split method separates strings by a specified set of characters and places these strings into an array of strings. For example, the following source code splits strArray based on ',' and stores all separated strings in an array.

string str1 = "ppp";
string str2 = "ccc";
string str3 = "kkk";
string strAll3 = str1 + ", " +str2+", "+str3 ;
string[] strArray = strAll3.Split(',');
foreach (string itm in strArray)
{
Console.WriteLine(itm.ToString() );
}

Uppercase and Lowercase
The ToUpper and ToLower methods convert a string in uppercase and lowercase respectively. These methods are easy to use. The following code shows how to use ToUppler and ToLower methods.

string aStr = "adgas";
string bStr = "ABNMDWER";
string strRes = aStr.ToUpper();
Console.WriteLine("Uppercase:"+ strRes.ToString());
strRes = bStr.ToLower();
Console.WriteLine("Lowercase:"+ strRes.ToString());
Formatting Strings

You can use the Format method to create formatted strings and concatenate multiple strings representing multiple objects. The Format method automatically converts any passed object into a string.

For example, the following code uses integer, floating number and string values and format them into a string using the Format method.

Listing 1: Using Format method to format a string

int val = 7;
string name = "Mr. John";
float num = 45.06f;
string str = String.Format ("Days Left : {0}. Current DataTime: {1:u}. \n String: {2}, Float: {3}" , val, DateTime.Now, name, num);
Console.WriteLine(str);
Trimming and Removing Characters from Strings

The String class provides Trim, TrimStart and TrimEnd methods to trim strings. The Trim method removes white spaces from the beginning and end of a string. The TrimEnd method removes characters specified in an array of characters from the end of a string and TrimStart method removes characters specified in an array of characters from the beginning of a string.

You can also use the Remove method to remove characters from a string. The Listing 2 code shows how to use these methods.

String str = " C# ";
Console.WriteLine("Hello{0}World!", str);
string trStr = str.Trim();
Console.WriteLine("Hello{0}World!", trStr );
str = "Hello World!";
char[] chArr = {'e', 'H','l','o',' ' };
trStr = str.TrimStart(chArr);
Console.WriteLine(trStr);
str = "Hello World!";
char[] chArr1 = {'e', 'H','l','o',' ' };
trStr = str.TrimEnd(chArr1);
Console.WriteLine(trStr);
string MyString = "Hello Delta World!";
Console.WriteLine(MyString.Remove(5,10));

Padding Strings

The PadLeft and PadRight methods can be used to pad strings. The PadLeft method right-aligns and pads a string so that its rightmost character is the specified distance from the beginning of the string. The PadRight method left-aligns and pads a string so that its rightmost character is a specified distance from the end of the string. These methods return new String objects that can either be padded with empty spaces or with custom characters. Listign 3 shows how to use these methods.

Listing 3: Using padding methods

string str1 = "My String";
Console.WriteLine(str1.PadLeft(20, '-'));
string str2 = "My String";
Console.WriteLine(str2.PadRight(20, '-'));