1. Chapter 3.3 Numeric Data Types and Variables

2. Slide 2 Objectives Create variables to store information while a solution runs Perform computations with variables using assignment statements Understand the role of precedence, perform type conversions, and format data Write a statement on multiple lines and calculate solution output

3. Slide 3 Storing Data in Variables Variable stores data while a solution runs A variable is simply a unique name that identifies a space in memory (RAM) Data may be a string of characters or a number Every variable has a data type A variable's data type determines the kind of information that the variable can store Numbers, characters, etc. Every variable has a name Use standard prefixes for variable names to denote data type

4. Slide 4 Variables A variable is a name that is used to refer to an item of data. The value assigned to the variable may change. Up to 16,838 characters long Begin with a letter or an underscore Consist of only letters,digits and underscores A Variable name is written in lowercase letters except for the first letters of additional words, such as costOfIT201.

5. Slide 5 Numeric VB.NET Data Types Data TypeStorage SizePrefixPossible Values Boolean2 bytesblnTrue or False Date8 bytesdatDates between 1/1/0001 and 12/31/9999 Short2 bytesshoPositive and negative whole numbers between –32768 and 32767 Integer4 bytesintPositive and negative whole numbers between –2,147,483,648 and 2,147,483,647 Long8 byteslngPositive and negative whole numbers

6. Slide 6 Numeric VB.NET Data Types Data TypeStorage SizePrefixPossible Values Single4 bytessngA number with at most 6 digits to the right of the decimal point Double8 bytesdblA number with at most 14 digits to the right of the decimal point String1 byte per character strCharacter string of up to about 2 billion characters

7. Slide 7 Standards for Variable Names Use a one-character prefix to denote scope The scope of a variable indicates which event handlers can use that variable Module-level variables carry a prefix of "m“ Global or Public variable carry a prefix of “g” Use a three-character prefix to denote data type

8. Slide 8 Standards for Variable Names Valid Variable Name Invalid Variable Name Cause mlngCountermlng.CounterA period (.) mintTotal A space mdblFutureValuemdlbFuture-ValueA dash (-) mdblGainmdbl*GainSpecial characters

9. Slide 9 Declaring a Variable Private statement declares variable Private varname As type [ = initialization expression] varname is variable name As type contains data type of variable Optional initialization expression contains the initial value of a variable Example: Declare variables having the Double and Integer data types Private mdblInterestRate As Double Private mintCounter As Integer

10. Slide 10 Declaring a Variable Initialize a variable when declaring it New to VB.NET Example: Declare a modular Integer variable and store the value 30 in the variable Private mintYearTerm As Integer = 30 Focus (m) Prefix (int) Name YearTerm

11. Slide 11 Declaring a Variable Do not include punctuation characters in a variable initialization The following declarations are illegal because of the $ sign and commas: Private mdblInitialValue As Double = 100, 000.52 Private mdblInitialValue As Double = $ 100, 000.52 Possible to declare multiple variables on the same line Private mintYearTerm, mintMonthTerm As Integer

12. Slide 12 Declaring Module-Level Variables Declare module-level variables after the statements generated by the Window Form Designer but outside an event handler

13. Slide 13 DIM Statement DIM statement declares variable DIM varname As type [ = initialization expression] varname is variable name As type contains data type of variable Optional initialization expression contains the initial value of a variable Example: Declare variables having the Double and Integer data types DIM mdblInterestRate As Double DIM mintCounter As Integer

14. Slide 14 Variable Initialization Numeric variables are automatically initialized to 0: Dim varName As Double To specify a nonzero initial value Dim varName As Double = 50

15. Slide 15 Multiple Declarations multiple-declaration statements : Dim a, b As Double Dim a As Double, b As Integer Dim c As Double = 2, b As Integer = 5

16. Slide 16 Arithmetic Operators Expressions consists of literal values, constants, variables and arithmetic operators An arithmetic operator performs a mathematical calculation Multiply the literal values 3 and 2 together and store the result (6) in the variable mintResult mintResult = 3 * 2 This is also called an assignment statement

17. Slide 17 Arithmetic Operators (2) Operators in Order of Precedence DescriptionExample ^Raises a number to the power of an exponent 2 ^ 3 is equal to 8 * /Multiplication and Division2 * 3 is equal to 6 8 / 4 is equal to 2 \Integer Division10 \ 3 is equal to 3 5 \ 2 is equal to 2 ModModulus arithmetic10 Mod 3 is equal to 1 + -Addition and subtraction2 + 3 is equal to 5

18. Slide 18 Arithmetic Operators – Example Divide two numbers and multiply the intermediate result by 100 Private mdblNumerator As Double = 10 Private mdblDenominator As Double = 5 Private mdblResult As Double mdblResult = mdblNumerator / mdblDenominator * 100

19. Slide 19 Arithmetic Operations Numbers are called numeric literals Five arithmetic operations in VB.NET + addition 3 + 2 - subtraction 3 - 2 * multiplication 3 * 2 / division 3 / 2 ^ exponentiation 3 ^ 2

20. Slide 20 The Role of Precedence Programming languages evaluate arithmetic expressions from left to right in a predefined order known as precedence Perform exponentiation first Next perform multiplication and division Next perform Integer division and then apply the Mod operator Next perform addition and subtraction Parenthesis override default precedence Parenthesis may be nested

21. Slide 21 Precedence (Example) (Var1 + Var2) / (Var3 + Var4) * (Var5 ^ Var6) 1 (addition)2 (addition)3 (exponent) 4 (division)5 (multiplication)

22. Slide 22 Variables Declaration: Dim dblSpeed As Double Variable name Data type Assignment: dblSpeed = 50

23. Slide 23 Increment variable value To add 1 to the numeric variable var var = var + 1 Or as a shortcut var +=1

24. Slide 24 Built-in Functions Functions associates with one or more values and returns a value(output) Math.sqrt(n): Returns the square root of n. Math.Sqrt(9) is 3 Int(n): Returns greatest integer less than or equal to n Int(9.7) is 9

25. Slide 25 Built-in Functions Math.Round(n, r): number n rounded to r decimal places Math.Round(2.317,1) is 2.3 Math.Round(2.7) is 3 When n is halfway between two successive whole number, then it rounds to the nearest even number Math.Round(2.5) is 2 Math.Round(3.5) is 4

26. Slide 26 Three Types of Errors Syntax error – grammatical errors misspellings, omissions, incorrect punctuation Run-time error occurs when program is running Logic error program doesn’t perform as it is intended

27. Slide 27 Type Conversion VB.NET must convert data from one data type to another when evaluating mathematical expressions The Option Strict On statement enables strict type checking Strict type checking requires explicit type conversion from less restrictive types to more restrictive types Use strict type checking to minimize hard to find errors resulting from implicit type conversion

28. Slide 28 Strict Type Checking (Example) The following statement will cause an error if strict type checking is enabled. If disabled, mintPI will store the value 3 Note that the result if the implicit type conversion is truncation Private mintPI As Integer = 3.14159

29. Slide 29 Option Explicit Option Explicit On statement requires that you declare variables before using them the first time Also reduces hard to find errors resulting from typos Note that Option Explicit and Option Strict statements appear at the beginning of a module

30. Slide 30 Type Conversion Methods Methods belong to the System.Convert class ToInt16 converts value to a Short ToInt32 converts value to an Integer ToInt64 converts value to a Long ToDouble converts value to a Double ToSingle converts value to a Single ToString converts value to a String Each method takes one argument; the value to convert Note that these methods supercede older intrinsic functions like CInt and CLng

31. Slide 31 Type Conversion Examples Private msngInput As Single = 3.44 Private mstrInput As String = "3.95“ ‘ why use “” Private mintOutput As Integer Private msngOutput As Single Convert a Single to an Integer mintOutput = System.Convert.ToInt32(msngInput) Convert a String to an Integer mintOutput = System.Convert.ToInt32(mstrInput) Convert a String to a Single msngOutput = System.Convert.ToSingle(mstrInput)

32. Slide 32 Numeric Overflow Numeric overflow occurs when trying to store too large a number in a variable The following statements will cause a numeric overflow error because the largest number that can be stored in a short is 32767 Private mshoExample As Short mshoExample = 46000 mshoExample = 2500 * 2500

33. Slide 33 Numeric Overflow VB.NET performs arithmetic using less restrictive type on right side of expression The last statement will cause numeric overflow: Private mshoArg1 As Short, mshoArg2 As Short Private mintArg3 As Integer mshoArg1 = 32000 mshoArg2 = 32000 mintArg3 = mshoArg1 * mshoArg2

34. Slide 34 Formatting a Numeric Value with Methods The ToString type conversion method accepts a string argument to format data Special characters are used to define the format lblGain.Text = mdblGain.ToString("$##,###.##") variable ToString method argument defines how to format the value

35. Slide 35 Formatting Placeholders CharacterDescription 0 Digit placeholder. If number corresponding to position does not contain a value, then a 0 appears # Digit placeholder. If number corresponding to position does not contain a value, then a space appears. Decimal placeholder. Defines the position of the decimal point, Thousands separator % Percentage placeholder - + $ ( ) Literal characters embedded in the format string

36. Slide 36 Formatting Examples Format String (Mask)ValueFormatted value 000000.000123.45000123.450 ###,###.001234.41,234.40 $###,###.001234.4$1,234.40 ###%0.088% ##.00%0.088.00% C1234.4$1234.40 F1234.41234.40

37. Slide 37 Creating Well-Written Comments A Comment is a full or partial line of text ignored by VB.NET Create comments to describe what your code is doing or how code performs a particular task Multiple comments are called a comment block Blank lines between statements are ignored and are called whitespace A comment can appear on its own line and begins with a single quote ( ' ) A comment can appear at the end of a line

38. Slide 38 Creating Well-Written Comments The following is a comment appearing on its own line: ' This line is a comment. The following comment appears at the end of a line. Note a space must precede the comment character txtDemo.text = "Dog" 'Store "Dog" in the text box Comment

39. Slide 39 Creating Well-Written Comments VB.NET displays comments in in green

40. Slide 40 Writing Assignment Statements Using Variables Store a property in a variable mintResult = txtExample.Height Store a literal value in a variable mintResult = 3 Store another variable in a variable mintResult = mintExample

41. Slide 41 Continuation Lines Use when statement will not fit on a line Underscore (_) is the continuation character Rules for use A Space ( ⇑ ) must precede the continuation character You cannot follow a continuation character with a Comment Do not break up words Multiple continuation lines allowed

42. Slide 42 Continuation Lines (Example) The following statement appears on two lines: mdblInterestRate = ⇑ _ System.Convert.ToDouble(txtInterestRate.Text) / 100