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Clearly Visual Basic: Programming with Visual Basic 2008

Clearly Visual Basic: Programming with Visual Basic 2008. Chapter 8 What’s Wrong with It?. Objectives. Locate syntax errors using the Error List window Locate a logic error by stepping through the code Locate logic errors using breakpoints Fix syntax and logic errors.

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Clearly Visual Basic: Programming with Visual Basic 2008

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  1. Clearly Visual Basic: Programming with Visual Basic 2008 Chapter 8 What’s Wrong with It?

  2. Objectives • Locate syntax errors using the Error List window • Locate a logic error by stepping through the code • Locate logic errors using breakpoints • Fix syntax and logic errors Clearly Visual Basic: Programming with Visual Basic 2008

  3. There’s a Bug in my Soup! • Downside to variables and named constants • Their use requires additional lines of code • Bug • Error in a program’s code • Debugging • Process of locating and correcting any bugs in a program • Program bugs • Typically caused by either syntax errors or logic errors Clearly Visual Basic: Programming with Visual Basic 2008

  4. Finding Syntax Errors • Syntax error • Occurs when you break one of the language’s rules • Code Editor • Detects most syntax errors as you enter instructions Clearly Visual Basic: Programming with Visual Basic 2008

  5. Locating Logic Errors • Logic error • Can occur for a variety of reasons • Difficult type of error to locate • Cannot be detected by Code Editor Clearly Visual Basic: Programming with Visual Basic 2008

  6. Locating Logic Errors (continued) • Debug the Discount application • Letter D at end of a value indicates value’s data type is Decimal Clearly Visual Basic: Programming with Visual Basic 2008

  7. Clearly Visual Basic: Programming with Visual Basic 2008

  8. Clearly Visual Basic: Programming with Visual Basic 2008

  9. Locating Logic Errors (continued) • Use a breakpoint to pause execution at a specific line in the code • Debug the Hours Worked application • .0 at end of a number indicates that number’s data type is Double Clearly Visual Basic: Programming with Visual Basic 2008

  10. Clearly Visual Basic: Programming with Visual Basic 2008

  11. Hawkins Solution

  12. Public Class frmMain Dim decBegin As Decimal Dim decEarned As Decimal Dim decSpent As Decimal Dim decEnding As DecimalPrivate Sub btnCalc_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnCalc.Click ' calculates the ending balance based on the beginning ' balance, amount earned, and amount spent ' assign input to variables Decimal.TryParse(txtBegin.Text, decBegin) Decimal.TryParse(txtSpent.Text, decSpent) ' calculate and display ending balance decEnding = decBegin + decEarned - decSpent lblEnding = decEnding.ToString("C2") End Sub End Class

  13. ' calculates and displays your weight on planets and the moon ' Jupiter is 2.54 times earth weight, Venus is .91, Mars is .38, moon is .17

  14. Public Class frmMain Dim dblEarth As Double Dim dblJupiter As Double: Dim dblVenus As Double Dim dblMars As Double: Dim dblMoon As DoublePrivate Sub btnCalc_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnCalc.Click ' calculates and displays your weight on planets and the moon ' Jupiter is 2.54 times earth weight, Venus is .91, Mars is .38, moon is .17 ' calculate weights dblJupiter = dblEarth * 2.54 : dblVenus = dblEarth * 0.91 dblMars = dblEarth * 0.38 : dblMoon = dblEarth * 0.17 ' display weights lblJupiter.Text = dblJupiter.ToString("N2") lblVenus.Text = dblVenus.ToString("N2") lblMars.Text = dblMars.ToString("N2") lblMoon.Text = dblMars.ToString("N2") End Class

  15. Martins Solution Answer should be $53.35

  16. Private Sub btnGainLoss_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnGainLoss.Click ' calculates and displays the gain or loss on a stock Dim intShares As Integer Dim decOpenPrice As Decimal Dim decClosePrice As Decimal Dim decGainLoss As Decimal ' assign input to variables Integer.TryParse(txtShares.Text, intShares) Decimal.TryParse(txtOpening.Text, decClosePrice) Decimal.TryParse(txtClosing.Text, decClosePrice) ' calculate and display gain or loss decGainLoss = decClosePrice - decOpenPrice * intShares lblGainLoss.Text = decGainLoss.ToString("C2") End Sub

  17. Summary • Program errors (bugs) • Caused by either syntax errors or logic errors • Syntax errors in an application’s code • Listed in Error List window when you start the application • You can locate logic errors by stepping through the code • Letter D at the end of a value • Indicates value’s data type is Decimal Clearly Visual Basic: Programming with Visual Basic 2008

  18. Summary (continued) • .0 at the end of a number • Indicates that the number’s data type is Double • Before viewing value stored in a control or variable • First consider the value you expect to find Clearly Visual Basic: Programming with Visual Basic 2008

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