1. Declaring and Using Variables Visual Basic Data Types

2. 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 intPopulationstrCity

3. 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

5. 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.

6. 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)

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

8. 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.

9. 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

10. 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 or picOutput.Print intNum1; "+"; intNum2; "="; intAnswer

11. PictureBox Cls Method PictureBoxes can have their contents removed with the Cls method: picOutput.Cls

12. Errors Syntax errors –usually grammatical errors or misspelling picAnswer.Primt intAnswer txtAnswer.txt = intFirstInput + intSecondInput Runtime errors –errors detected while the program is running dblAnwer = 1/intFirstInput Logical errors –errors which occurs when the program does not run as intended dblAverage = intFirstInput + intSecondInput/2