Computer Programming Concepts and Visual Basic David I. Schneider

134 Computer Programming Concepts and Visual Basic
If UCase(txtName.Text) = “SECRET.TXT”Then
Do
passWord = InputBox(“What is the password?”)
passWord = UCase(passWord)
Loop Until passWord = “SHAZAM”
End If
Open txtName.Text For Input As #1
Input #1, info
picItem.Cls
picItem.Print info
Close #1
End Sub
Do loops allow us to calculate useful quantities for which we might not know a simple
formula.
EXAMPLE 4
Suppose you deposit $100 into a savings account and let it accumulate at 7 percent interest compounded
annually. The following program determines when you will be a millionaire.
Object Property Setting
frmInterest Caption 7% Interest
lblAmount Caption Amount Deposited
txtAmount Text (blank)
cmdYears Caption Years to become a
millionaire
picWhen
Private Sub cmdYears_Click()
Dim balance As Single, numYears As Integer
‘Compute years required to become a millionaire
picWhen.Cls
balance = Val(txtAmount.Text)
numYears = 0
Do While balance < 1000000
balance = balance + .07 * balance
numYears = numYears + 1
Loop
picWhen.Print “In”; numYears; “years you will have a million dollars.”
End Sub
[Run, type 100 into the text box, and press the command button.]
COMMENTS
1. Be careful to avoid infinite loops—that is, loops that are never exited. The following
loop is infinite, because the condition “num < > 0”will always be true.
Note: The loop can be terminated by pressing Ctrl+Break.