C#: Introduction for Developers

1. Neal Stublen nstublen@jccc.edu C#: Introduction for Developers

2. C# Data Types

3. Built-in Types • Integer Types • byte, sbyte, short, ushort, int, uint, long, ulong • Floating Point Types • float, double, decimal • Character Type • char (2 bytes!) • Boolean Type • bool (true or false) • Aliases for .NET data types (Byte, Integer, Decimal, etc.)

4. Declare and Initialize <type> <variableName>; int index; float interestRate; <type> <variableName> = <value>; int index = 0; float interestRate = 0.0005;

5. Constants const <type> <variableName> = <value>; const decimal PI = 3.1415926535897932384626;

6. Naming Conventions • Camel Notation (camel-case) • salesTax • Common for variables • Pascal Notation (title-case) • SalesTax • Common for type names and constants • C or Python style • sales_tax (variable) • SALES_TAX (constant) • Not common

7. Arithmetic Operators • Addition (+) • Subtraction (-) • Multiplication (*) • Division (/) • Modulus (%) • Increment (++) • Decrement (--)

8. Assignment Operators • Assignment (=) • Addition (+=) • Subtraction (-=) • Multiplication (*=) • Division (/=) • Modulus (%=)

9. Type Casting • Implicit • Less precise to more precise • byte->short->int->long->double int letter = 'A';int test = 96, hwrk = 84;double avg = test * 0.8 + hwrk * 0.2;

10. Type Casting • Explicit • More precise to less precise • int->char, double->float (<type>) <expression> double total = 4.56; intavg = (int)(total / 10); decimal decValue = (decimal)avg;

11. What Should Happen? inti = 379; double d = 4.3; byte b = 2; double d2 = i * d / b; int i2 = i * d / b;

12. "Advanced" Math Operations • totalDollars = Math.Round(totalDollars, 2); • hundred = Math.Pow(10, 2); • ten = Math.Sqrt(100); • one = Math.Min(1, 2); • two = Math.Max(1, 2);

13. Strings • string text = "My name is "; • text = text + "Neal" • text += " Stublen." • double grade = 94; • string text = "My grade is " + grade + “.”;

14. Special String Characters • Escape sequence • New line ("\n") • Tab ("\t") • Return ("\r") • Quotation ("\"") • Backslash ("\\") • filename = "c:\\dev\\projects"; • quote = "He said, \"Yes.\""; • filename = @"c:\dev\projects"; • quote = @"He said, ""Yes.""";

15. Converting Types • <value>.ToString(); • <type>.Parse(<string>); • Convert.ToBool(<value>); • Convert.ToString(<value>); • Convert.ToInt32(<value>);

16. Formatted Strings • <value>.ToString(<formatString>); • amount.ToString("c"); // $43.16 • rate.ToString("p1"); // 3.4% • count.ToString("n0"); // 2,345 • String.Format("{0:c}", 43.16); // $43.16 • String.Format("{0:p1}", 0.034); // 3.4% • See p. 121 for formatting codes

17. Variable Scope • Scope limits access and lifetime • Class scope • Method scope • Block scope • No officially "global" scope

18. Enumeration Type enum StoplightColors {     Red,     Yellow,     Green }

19. Enumeration Type enum StoplightColors {     Red = 10,     Yellow,     Green }

20. Enumeration Type enum StoplightColors {     Red = 10,     Yellow = 20,     Green = 30 }

21. Enumeration Type enum StoplightColors {     Red = 10 } string color = StoplightColors.Red.ToString();

22. "null" Values • Identifies an unknown value • string text = null; • int? nonValue = null; • bool defined = nonValue.HasValue; • int value = nonValue.Value; • decimal? price1 = 19.95; • decimal? price2 = null; • decimal? total = price1 + price2;

23. Control Structures • Boolean expressions • Evaluate to true or false • Conditional statements • Conditional execution • Loops • Repeated execution

24. Boolean Expressions • Equality (==) • a == b • Inequality (!=) • a != b • Greater than (>) • a > b • Less than (<) • a < b • Greater than or equal (>=) • a >= b • Less than (<=) • a <= b

25. Logical Operators • Combine logical operations • Conditional-And (&&) • (file != null) && file.IsOpen • Conditional-Or (||) • (key == 'q') || (key == 'Q') • And (&) • file1.Close() & file2.Close() • Or (|) • file1.Close() | file2.Close() • Not (!) • !file.Open()

26. Logical Equivalence • DeMorgan's Theorem • !(a && b) is the equivalent of (!a || !b) • !(a || b) is the equivalent of (!a && !b)

27. if-else Statements if (color == SignalColors.Red) { Stop(); } else if (color == SignalColors.Yellow) { Evaluate(); } else if (color == SignalColors.Green) { Drive(); }

28. switch Statements switch (color ) { case SignalColors.Red: { Stop(); break; } case SignalColors.Yellow: { Evaluate(); break; } default: {           Drive(); break; } }

29. while Statements while (!file.Eof) { file.ReadByte(); } char ch; do { ch = file.ReadChar(); } while (ch != 'q');

30. for Statements int factorial = 1; for (inti = 2; i <= value; ++i) {     factorial *= i; } string digits = "" for (char ch = '9'; ch <= '0'; ch-=1) {     digits += ch; }

31. break and continue Statements string text = ""; for (int i = 0; i < 10; i++) {     if (i % 2 == 0)         continue;     if (i > 8)         break;     text += i.ToString(); }

32. Caution! int index = 0; while (++index < lastIndex) { TestIndex(index); } int index = 0; while (index++ < lastIndex) { TestIndex(index); }

33. What About This? for (int i = 0; i < 10; i++) { } for (int i = 0; i < 10; ++i) { }

34. Debugging Loops

35. Debugging Summary • Stepping through code (over, into, out) • Setting breakpoints • Conditional breakpoints

36. Class Methods class DiscountCalculator {     private decimal CalcDiscPercent(decimal inAmt)     {         return (inAmt > 250.0m) ? 0.10m: 0.0m;     }     public decimal CalcDiscAmount(decimal inAmt)     {         decimal percent = CalcDiscPercent(inAmt);         return inAmt * percent;     } }

37. Passing Parameters

38. Parameters Summary • Pass zero or more parameters • Parameters can be optional • Optional parameters are "pre-defined" using constant values • Optional parameters can be passed by position or name • Recommendation: Use optional parameters cautiously

39. Parameters Summary • Parameters are usually passed by value • Parameters can be passed by reference • Reference parameters can change the value of the variable that was passed into the method

40. Events and Delegates

41. Event and Delegate Summary • A delegate connects an event to an event handler. • The delegate specifies the handler’s return type and parameters. • Event handlers can be shared with multiple controls

42. Exceptions and Validation

43. Exceptions Exception Format Exception Format Exception Arithmetic Exception Arithmetic Exception

44. Format Exception string value = “ABCDEF”; int number = Convert.ToInt32(value);

45. Overflow Exception checked { byte value = 200; value += 200; int temp = 5000; byte check = (byte)temp; }

46. “Catching” an Exception try { int dividend = 20; int divisor = 0; int quotient = dividend / divisor; int next = quotient + 1; } catch { }

47. Responding to Exceptions • A simple message box: • MessageBox.Show(message, title); • Set control focus: • txtNumber.Focus();

48. Catching Multiple Exceptions try {} catch( FormatException e) { } catch(OverflowException e) { } catch(Exception e) { } finally { }

49. Throwing an Exception throw new Exception(“Really bad error!”); try { } catch(FormatException e) { throw e; }