1. Text Files and String Processing

2. The Char Struct For documentation
Help > Search. Look for: Char Structure
Filtered by:
Language: Visual C#
Technology: .NET Development
Content Type: Documentation & Articles
Double click on Char Structure in Search Results.

3. The Char Struct
The Char value type represents a Unicode character (aka Unicode code point)
Implemented as a 16-bit number ranging in value from hexadecimal 0x0000 to 0xFFFF.
See

4. The Char Struct Examples (from the help page) char chA = 'A';
string str = "test string";
Examples of char methods on the next slide use these examples as arguments.
Note: Single quotes around char literal.
Note: Double quotes around string literal.

5. Static Methods of the Char Struct
Console.WriteLine(chA.CompareTo('B')); // Output: "-1"
Console.WriteLine(chA.Equals('A')); // Output: "True"
Console.WriteLine(Char.GetNumericValue(ch1)); // Output: "1"
Console.WriteLine(Char.IsControl('\t')); // Output: "True"
Console.WriteLine(Char.IsDigit(ch1)); // Output: "True"
Console.WriteLine(Char.IsLetter(',')); // Output: "False"
Console.WriteLine(Char.IsLower('u')); // Output: "True"
Console.WriteLine(Char.IsNumber(ch1)); // Output: "True"
Console.WriteLine(Char.IsPunctuation('.')); // Output: "True"
Console.WriteLine(Char.IsSeparator(str, 4)); // Output: "True"
Console.WriteLine(Char.IsSymbol('+')); // Output: "True"
Console.WriteLine(Char.IsWhiteSpace(str, 4)); // Output: "True"
Console.WriteLine(Char.Parse("S")); // Output: "S"
Console.WriteLine(Char.ToLower('M')); // Output: "m"
Console.WriteLine('x'.ToString()); // Output: "x"

6. The String Class For documentation search for String Class
Help, Search for: "String Class"
Filtered by:
Language: Visual C#
Technology: .NET Development
Content Type: Documentation & Articles
Double click on String Class in Search Results.

7. Finding Documentation

8. String Class Documentation

9. The String Class Class String vs "strings"
A String object is a sequential collection of System.Char structs that represents a string.
The value of the String is the content of the sequential collection, and the value is immutable.
Methods that appear to modify a String actually return a new String containing the modification.

10. String vs string
As types, System.String and string are interchangeable.
In C# string is an alias for System.String.
We normally don’t need to prefix String with System because most C# programs have the line
using System;

11. String vs string static void Main(string[] args) {
string s = "This is a string";
Console.WriteLine(s);
String S = "This is a String";
Console.WriteLine(S);
Console.ReadLine(); }

12. Character strings enclosed in double quotes are string literals.
Compare to C/C++
String S1 = "This is a String";
Some characters have special interpretation in string literals:
\t is replaced by a tab character
\" is replaced by a quote character (rather than ending the string)
\\ is replaced by a backslash character

13. String Literals
If you don’t want escape character processing, in front of the quoted string.
Called a verbatim literal.
S1 is a string with a backslash \"
This is frequently done in Microsoft examples.
Especially nice for Windows file path strings, which include backslash characters.

14. String Literal Documentation

15. String Literal Documentation

16. String Operations The String class provides a rich set of operations:
Substring
Concatination
Length
Comparison
If you need to do it, there is probably a built-in operation for it.
Click on the “Methods” link in the documentation page for String Class.

17. String Methods Documentation

18. Example: Converting to Upper Case
static void Main(string[] args) {
String S1 is a string with a backslash \";
Console.WriteLine(S1);
Console.WriteLine("Converting S1 to Upper Case");
S1.ToUpper();
Console.WriteLine("Here is the result:");
Console.ReadLine(); }
Caution: This code is (intentionally) incorrect.

19. Converting to Upper Case
What’s wrong here?

20. String Function Used Correctly
static void Main(string[] args) {
String S1 is a string with a backslash \";
Console.WriteLine (S1);
Console.WriteLine ("Converting S1 to Upper Case");
String S2 = S1.ToUpper();
Console.WriteLine ("Here is the result:");
Console.WriteLine (S2);
Console.ReadLine(); }

21. String Function Used Correctly

22. String Operations Ordinal Linguistic
acts on the numeric value of each Char object
Linguistic
acts on the value of the String taking into account culture-specific casing, sorting, formatting, and parsing rules.
Ordinal operations use the binary value of the chars
Linguistic operations execute in the context of an explicitly declared culture or the implicit current culture.
Typically work as you would expect them to.

23. Example: Cuture Sensitive Compare

24. Example: Numeric Compare

25. Comparing Strings class Program { static void Main(string[] args)
string S1 is a string with a backslash \";
Console.WriteLine(S1);
Console.WriteLine("Converting S1 to Upper Case");
string S2 = S1.ToUpper();
Console.WriteLine("Here is the result:");
Console.WriteLine(S2);
int i1 = String.Compare(S1, S2);
Console.WriteLine("Compare(S1, S2) = {0}", i1);
int i2 = String.CompareOrdinal(S1, S2);
Console.WriteLine("CompareOrdinal(S1, S2) = {0}", i2);
Console.ReadLine(); }

26. Comparing Strings

27. Using Operators if (S1 == S2) {
Console.WriteLine("S1 and S2 are equal"); }
else
Console.WriteLine("S1 and S2 are not equal");

28. Using Operators

29. Using Operators if (S1 < S2) {
Console.WriteLine("S1 is less than S1"); }
else
Console.WriteLine("S1 is not less than S1");

30. Using Operators We can use the == operator with strings.
But not < and >.
Remember that == for reference types normally checks if the operands are references to the same object.
Class string overrides the operator inherited from class System.Object.
Compares the contents of the operands.

31. Operations on Strings
All numeric types provide a Parse static method that converts a string into the numeric value.
String strZip; // Zip code as string
int intZip; // Zip code as integer
...
intZip = int.Parse(strZip);
Will throw an exception if the string is not the representation of a number of the specified type.

32. tryParse
Numeric types also have a tryParse method that will not throw an exception when the string is not a valid number.
static void Main(string[] args) {
String strZip = Console.ReadLine();
int intZip;
if (int.TryParse(strZip, out intZip))
Console.WriteLine(strZip + " is a valid integer"); }
else
Console.WriteLine(strZip + " is not a valid integer");

33. Parsing Integers

34. Comma Separated Values
Common way to represent structured data in a text file.
Example:
Doe,John,1234 Oak St.,Marion,OH,22333
Frequently used as interchange format for spreadsheet and database programs.

35. The String.Split Method
For documentation
Help > Search. Look for: Split
Double click on “String.Split Method” in Search Results.

36. String.Split Example static void Main(string[] args) {
string words = "one,two,three,four";
string[] split;
split = words.Split(',');
foreach (string s in split)
Console.WriteLine(s); }
Console.ReadLine();
Note: Char

37. String.Split Example

38. The String.Join Method static void Main(string[] args) {
String[] fruits = {"apple", "orange", "grape", "pear"};
String result = String.Join ( ",", fruits);
Console.WriteLine (result);
Console.ReadLine(); }
Note: String, not char

39. The String.Join Method

40. Operations Producing Strings
Every class has a ToString() method
Inherited from Class object
Default is Namespace.ClassName
Should override the default in your own class definitions.
Include a meaningful version in class definition.

41. Example: Circle.ToString()
class Circle : Shape {
double radius;
public Circle(double radius_arg, String name_arg) :
base (name_arg)
this.radius = radius_arg; }
public double Radius()
return radius;
public override String ToString()
return "I am a Circle of radius " +
radius.ToString() +
" by the name of " + name;
End of Section

42. Text Files For documentation Help > Search. Look for: text file i/o
Filtered by:
Language: Visual C#
Technology: .NET Development
Content Type: Documentation & Articles
Double click on “Basic File I/O” in Search Results.

43. Writing a Text File static void Main(string[] args) {
String[] text_array = new String[4];
text_array[0] = "This is the first line";
text_array[1] = "This is the second line";
text_array[2] = "Line \t with \t some \t tabs";
text_array[3] with a backslash \";
System.IO.StreamWriter Writer =
new System.IO.StreamWriter
foreach (String S in text_array)
Writer.WriteLine(S); }
Writer.Close();
Console.WriteLine C:\test.txt written");
Console.ReadLine();

44. Running Text File Demo Program

45. Look at the File

46. Reading a Text File String Input_Line; using System.IO; ...
static void Main(string[] args) {
String Input_Line;
StreamReader Reader = new
while ((Input_Line = Reader.ReadLine()) != null)
Console.WriteLine(Input_Line); }
Console.ReadLine();

47. Program Running

48. Summary Class String is extraordinarily complex
but we can usually ignore the complexity
Typically will do what we expect.
Provides built-in methods to do whatever we need.
Reading and Writing sequential text files in C# is easy.
“Open” operation is replaced by instantiating a StreamReader or StreamWriter.
Use that object to read or write the file one line at a time.
Be sure to call Close() method when finished.
End of Section