Neal Stublen Tonight’s Agenda  C# data types  Control structures  Methods and event handlers  Exceptions and validation  Q&A.

Neal Stublen nstublen@jccc.edu

Tonight’s Agenda  C# data types  Control structures  Methods and event handlers  Exceptions and validation  Q&A

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.)

Declare and Initialize ; int index; float interestRate; = ; int index = 0; float interestRate = 0.0005;

Constants const = ; const decimal PI = 3.1415926535897932384626; PI = 3.14; // error!!

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 (variables) SALES_TAX (constants) Not common

Arithmetic Operators  Addition (+)  Subtraction (-)  Multiplication (*)  Division (/)  Modulus (%)  Increment (++) value++ or ++value  Decrement (--) value-- or --value

Prefix and Postfix Operators  Prefix operators modify a variable before it is evaluated  Postfix operators modify a variable after it is evaluated y = 1; x = y++; // y = 2 // x = 1 (y was incremented AFTER evaluation) y = 1; x = ++y; // y = 2 // x = 2 (y was incremented BEFORE evaluation)

Assignment Operators  Assignment (=)  Addition (+=) x = x + y → x += y  Subtraction (-=)  Multiplication (*=)  Division (/=)  Modulus (%=)

Order of Precedence  Increment, decrement Prefix versions  Negation  Multiplication, division, modulus  Addition, subtraction  Evaluate from left to right  Evaluate innermost parentheses first

What Should Happen? int i = (54 – 15) / 13 - 7; int i = 39 / 13 - 7; = 3 - 7; = -4;

What Should Happen? int i = a++ * 4 – b; int i = (a * 4) - b; a = a + 1;

What Should Happen? int i = ++a * 4 – b; a = a + 1; int i = (a * 4) - b;

"Advanced" Math Operations  The Math class provides a set of methods for common math operations  totalDollars = Math.Round(totalDollars, 2); Rounds to nearest whole number  hundred = Math.Pow(10, 2);  ten = Math.Sqrt(100);  one = Math.Min(1, 2);  two = Math.Max(1, 2);

String Declarations // Simple declaration string text; // Initial value (double quotes) string text = "Hello!"; // Empty string string text = ""; // Unknown value (not an empty string) string text = null;

String Concatenation string text = "My name is "; text = text + "Neal" text += " Stublen.“ string first = "Neal"; string last = "Stublen"; string greeting = “Hi, " + first + " " + last; double grade = 94; string text = "My grade is " + grade + ".";

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.""";

Type Casting  Implicit Less precise to more precise  byte->short->int->long->double  Automatic casting to more precise types int letter = 'A'; int test = 96, hmwrk = 84; double avg = tests * 0.8 + hmwrk * 0.2;

Type Casting  Explicit More precise to less precise  int->char, double->float  Must be specified to avoid compiler errors ( ) double total = 4.56; int avg = (int)(total / 10); decimal decValue = (decimal)avg;

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

Converting Types To Strings  Everything has a ToString() method.ToString(); int i = 5; string s = i.ToString(); // s = "5“ double d = 5.3; string s = d.ToString(); // s = "5.3"

Converting Strings To Types  Use the data type’s Parse() method.Parse( ); ○ decimal m = Decimal.Parse("5.3");  Use the Convert class Convert.ToInt32( ); ○ int i = Convert.ToInt32(" Convert.ToBool( ); Convert.ToString( );...

Formatted Strings  Formatting codes can customize the output of ToString().ToString( ); amount.ToString("c"); // $43.16 rate.ToString("p1"); // 3.4% count.ToString("n0"); // 2,345  See p. 121 for formatting codes

Formatted Strings  String class provides a static Format method {index:formatCode} String.Format("{0:c}", 43.16); ○ // $43.16 String.Format("{0:p1}", 0.034); ○ // 3.4%

Formatted Strings  String.Format( "Look: {0:c}, {1:p1}", 43.16, 0.034); // Look: $43.16, 3.4%  String.Format( “{0}, your score is {1}.", name, score); // John, your score is 34.

Variable Scope  Scope limits access and lifetime  Class scope  Method scope  Block scope  No officially "global" scope

Enumeration Types  Enumerations define types with a fixed number of values enum StoplightColors { Red, Yellow, Green }

Enumeration Type  Numeric values are implied for each enumerated value enum StoplightColors { Red = 10, Yellow, Green }

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

Enumeration Type enum StoplightColors { Red = 10 } string color = StoplightColors.Red.ToString(); // color = "Red", not "10"

"null" Values  Identifies an unknown value  string text = null;  int value = null; // error!  int? nonValue = null;  bool defined = nonValue.HasValue;  int value = nonValue.Value;  decimal? price1 = 19.95m;  decimal? price2 = null;  decimal? total = price1 + price2; total = null (unknown, which seems intuitive)

Form Enhancements  Display a formatted subtotal as a currency  Round the discount amount to two decimal places  Keep running invoice totals  Reset the totals when the button is clicked  Chapter 4 exercises

Common Control Structures  Boolean expressions Evaluate to true or false  Conditional statements Conditional execution  Loops Repeated execution

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

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()

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

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

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

switch Statements switch (color) { case SignalColors.Red: { Stop(); break; } case SignalColors.Yellow: // fall through default: { Drive(); break; }

switch Statements switch (color) { case SignalColors.Red: // fall through case SignalColors.Yellow: // fall through default: { Drive(); break; }

switch Statements switch (name) { case "John": case "Johnny": case "Jon": {... break; }

Form Enhancements  Select a discount tier based on the customer type Chapter 5 exercises

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

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

break and continue Statements  break allows is to jump out of a loop before reaching its normal termination condition  continue allows us to jump to the next iteration of a loop

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(); }

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

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

Debugging Summary  Stepping through code (over, into, out)  Setting breakpoints  Conditional breakpoints

Form Enhancements  Examine the looping calculation in the Future Value example Chapter 5 exercises

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; }

Access Modifier 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; }

Return Type 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; }

Method Name 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; }

Method Parameters 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; }

Return Statements 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; }

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

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

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 Chapter 6, Exercise 1 Clear result when any value changes

Exceptions Exception Format ExceptionArithmetic ExceptionOverflowExceptionDivideByZeroException

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

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

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

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

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

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

Form Enhancements  What exceptions might occur in the future value calculation? Chapter 7 exercises

Neal Stublen Tonight’s Agenda  C# data types  Control structures  Methods and event handlers  Exceptions and validation  Q&A.

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Neal Stublen Tonight’s Agenda  C# data types  Control structures  Methods and event handlers  Exceptions and validation  Q&A.

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