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Declaring and Using Variables

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

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Declaring and Using Variables

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  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 • intPopulation strCity

  3. Declaring Variables • To declare a variable you use the Dimstatement. • Syntax: • Dim variablename [As datatype] • Examples: • Dim strFname As String • Dim strLname As String • Dim strFname, strLname As String

  4. 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.

  5. 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)

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

  7. 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.

  8. 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

  9. 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

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

  11. 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

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