C#: INTRODUCTION

FOR DEVELOPERS

Neal Stublennstublen@jccc.edu

C# Data Types

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

<type> <variableName>;int index;float interestRate;

<type> <variableName> = <value>;int index = 0;float interestRate = 0.0005;

Constants

const <type> <variableName> = <value>;

const decimal PI = 3.1415926535897932384626;

Naming Conventions Camel Notation (camel-case)

salesTaxCommon for variables

Pascal Notation (title-case)SalesTaxCommon for type names and constants

C or Python stylesales_tax (variable)SALES_TAX (constant)Not common

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

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

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;

Type Casting Explicit More precise to less precise int->char, double->float

(<type>) <expression>

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;

"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);

Strings string text = "My name is "; text = text + "Neal" text += " Stublen." 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.""";

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

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

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

Enumeration Typeenum StoplightColors{    Red,    Yellow,    Green}

Enumeration Typeenum StoplightColors{    Red = 10,    Yellow,    Green}

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

Enumeration Typeenum StoplightColors{    Red = 10}

string color =

  StoplightColors.Red.ToString();

"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;

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

switch Statementsswitch (color ){case SignalColors.Red:

    {        Stop();        break;    }case SignalColors.Yellow:

    {        Evaluate();        break;    }default:

    {          Drive();

        break;    }}

while Statementswhile (!file.Eof){    file.ReadByte();}

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

for Statementsint 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 Statementsstring 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 Loops

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

Class Methodsclass 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;    }}

Passing Parameters

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

Events and Delegates

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

Exceptions and Validation

ExceptionsException

Format Exception Arithmetic Exception

Format Exception Arithmetic Exception

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

Overflow Exceptionchecked{ byte value = 200; value += 200;

int temp = 5000; byte check = (byte)temp;}

“Catching” an Exceptiontry{ 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 Exceptionstry {}catch( FormatException e){}catch(OverflowException e){}catch(Exception e){}finally{}

Throwing an Exceptionthrow new Exception(“Really bad error!”);

try{}catch(FormatException e){ throw e;}