EXTRACT SUBSTRINGS

String extractions are a very common task in your programs. For example, a source string may contain blank spaces at the beginning or end of a string, and

you only want the contents between those blank spaces. Or, you may know the format of the string and want to obtain only a section of that string.

.NET Framework provides methods for extracting substrings that exist as individual characters or as a range of characters in a string. You have a few framework classes that allow string extractions. These classes are String,

StringBuilder, and RegularExpressions. The class that you use depends on how sophisticated your extraction needs to be.

The String class holds an immutable string of characters.

Each of these characters has an index, which is the position within the array of characters. The positions are tracked from left to right with the zero index being the first position (zero-based). If you know the starting index and (optionally) the length, you can pull out the desired substring.

If you desire to extract a single character, you can reference by the index in the String or StringBuilder object (for example, char cThirdChar = sMyString[2]; would extract the third character in the string sMyString).

‹ Rename the class name to

Extract.

› Add the Main function.

ˇ Save the file.

Á Create a string array of size 4 and initialize the array.

‡ Declare and initialize an integer and a string for outputting the images.

° Prompt the user for the format of the photos to view.

· Use a foreach statement to loop and display each of the photo names.

‚ Write a question mark to format the prompt message to the user.

You can use part of one string to build another string.

TYPE THIS:

using System; namespace StringSample

{class Extract

{static void Main(string[] args)

{string sPhoto = "src_fmlyreunion_jan2001_001.jpg"; string sFilePrefix;

string sBasePhoto =sPhoto.Substring(4); Console.WriteLine(sBasePhoto); Console.WriteLine("Please choose format to view?"); Console.WriteLine("[0]Low Resolution"); Console.WriteLine("[1]High Resolution"); Console.Write("?: ");

string sSelection = Console.ReadLine(); switch (sSelection)

{case "0" :

sFilePrefix = "lri_"; break; case "1" :

sFilePrefix = "hri_"; break; default :

sFilePrefix = "src_"; break;}

string sFullFile = sFilePrefix + sBasePhoto; Console.WriteLine("You will view {0}", sFullFile);

}}}

RESULT:

C:\>csc ExtractSubstrings_ai.cs C:\> ExtractSubstrings_ai.exe fmlyreunion_jan2001_001.jpg Please choose format to view? [0]Low Resolution

[1]High Resolution ?: 1

You will view hri_fmlyreunion_ jan2001_001.jpg

C:\>

— Create an integer variable and initialize the variable.

± Use a switch statement and the SubString function to read the prefix for the filename.

¡ For the case of hri, lri, and default, set the string variable.

You may not always receive a string from the user of your application with the required case to enter the string into your database. For example, you may have

user names in your database stored in all caps. The String class helps you change the case of your strings by providing the String.ToLower and the String.ToUpper methods.

The String.ToLower method changes any capital letters in the string to lowercase letters and returns the lowercase string so you can use it in another part of your program.

You can add an original string to the method or you can reference another string in your program.

The String.ToUpper method is the exact opposite of the

String.ToLower method. You use the String.ToUpper

method for converting any lowercase characters in a string to capital letters. Also like the String.ToLower method, you can include either an original string within the method or you can reference another string that references the

String class.

When you use the String.ToLower and String.ToUpper methods, Visual C# converts all of the characters in your string to either loweror uppercase letters and returns a copy of the string but does not change the string itself. If you want to change specific characters in your string, you should use the String.Replace method instead.

Capitalizing proper nouns, like names, would require changing the case of the initial character. Here is an example of doing capitalization on the initial character of a word.

TYPE THIS:

using System; namespace StringSample

{class InitialCaps

{static void Main()

{string sFullName = "joE mARkiewiCz"; string [] sNameParts =

sFullName.Split(char.Parse(" ")); string [] sNewParts = new string[2]; int iCount = 0;

foreach (string sPart in sNameParts)

{

sNewParts[iCount] = sPart[0].ToString().ToUpper() + sPart.Substring(

1,(sPart.Length - 1)).ToLower(); iCount++;

}

string sNewFullName = String.Join(" ",sNewParts); Console.WriteLine("Applying the custom intitial "

+"caps formatting on '{0}' give the following "

+"result: {1}", sFullName, sNewFullName);

}}}

RESULT:

C:\>csc

ChangeCase_ai.cs

C:\>

ChangeCase_ai.exe

Applying the custom intitial caps formatting on 'joE mARkiewiCz'

gives the following result: Joe Markiewicz

C:\>

‡ Use the ToUpper function to convert the message to uppercase and output the message to the console.

° Set a debug stop.