Declaring and Using Variables

Visual Basic Data Types

Naming Conventions

• Variables need to be assigned a data type and a name.

• The name should help you remember both the data type and purpose of the variable.

• Variable names can consist only of letters, digits, and underscores

intPopulation strCity

Declaring Variables• To declare a variable you use the Dim

statement.• Syntax:

Dim variablename [As datatype]

• Examples: Dim strFname As String Dim strLname As String Dim strFname, strLname As String

Type Stores Memory RangeByte (byt) Binary

numbers1 byte 0 to 255

Boolean (bln) Logical values 2 bytes true or false

Integer (int) Integers 2 bytes +/-32,768

Long (lng) Integers 4 bytes +/- 2 billion

Single (sng) Floating-pointnumbers

4 bytes -1E-45 to3E38

Double (dbl) Floating-pointnumbers

8 bytes -5E-324 to1.8E308

Currency(cur)

Numbers 8 bytes +/- 9E14

Date (dtm) Date and timeinformation

8 bytes Jan. 1, 100 -Dec. 31, 9999

Object (obj) Objectreference

4 bytes

String (str) Text 1 byte percharacter

Variant (vnt) Any data type Minimum16 bytes

Option Explicit

• To require variable declaration, include the Option Explicit statement in the General Declarations section of a form or module.

• If you try to use a variable that you have not declared when Option Explicit is set, you will receive a run-time error.

Conversion Functions

• Val() function converts a string to a number Dim intDegrees As Integer intDegrees = Val(txtTemp.Text)

• Str() functions converts a number to a string lblTemp.Caption = Str(intDegrees)

Calculations ^ exponentiation - negation *, / multiplication and division \ integer division Mod modulus arithmetic +, - addition and subtraction Use parentheses to override the order of

precedence.

Assigning Values to Variables

• If var is a variable, then the statement var = expression

first evaluates the expression on the right and then assigns it’s value to the variable.

Example

Private Sub cmdCaluate_Click() Dim intNum1 As Integer Dim intNum2 As Integer Dim intAnswer As Integer intNum1 = Val(txtFirstInput.Text) intNum2 = Val(txtSecondInput.Text) intAnswer = intNum1 ^ intNum2 picAnswer.Print intAnswer End Sub

PictureBox Print Method

• PictureBoxes can be used for output with the Print method:picAnswer.Print intNum1

picAnswer.Print intNum2

• Use a semicolon to print on the same line:picAnswer.Print intNum1;

picAnswer.Print intNum2

orpicOutput.Print intNum1; "+"; intNum2; "="; intAnswer

PictureBox Cls Method

• PictureBoxes can have their contents removed with the Cls method:picOutput.Cls

Errors

• Syntax errors– usually grammatical errors or misspellingpicAnswer.Primt intAnswertxtAnswer.txt = intFirstInput + intSecondInput

• Runtime errors– errors detected while the program is runningdblAnwer = 1/intFirstInput

• Logical errors– errors which occurs when the program does not run as intendeddblAverage = intFirstInput + intSecondInput/2