How do I change this For... Next statementinto a Do...Loop

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VB

Const intTERM As Integer = 5
        Dim dblPrincipal As Double
        Dim dblPayment As Double
        Dim blnIsConverted As Boolean

        lblPayments.Text = String.Empty
        blnIsConverted = _
            Double.TryParse(txtPrincipal.Text, dblPrincipal)

        If blnIsConverted Then
              For dblRate As Double = 0.05 To 0.1 Step 0.01
                dblPayment = -Financial.Pmt(dblRate / 12, intTERM * 12, dblPrincipal)
                lblPayments.Text = lblPayments.Text & _
                dblRate.ToString("P0") & "->" _
                & dblPayment.ToString("C2") & _
                ControlChars.NewLine
           Next dblRate

When I put in Do....Loop it says dblRate is not declared

Posted 6-Apr-14 12:10pm

Member 10728901

Updated 6-Apr-14 12:17pm

Wes Aday

v2

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[no name] 6-Apr-14 18:19pm

dblRate is only declared within the scope of the For loop. And there is no Do-While loop anywhere in your code.

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**Dalek Dave** · Answer 1 · 2014-04-06T12:16:00

That is because dblRate is NOT declared!

VB

Dim dblPrincipal As Double
Dim dblPayment As Double
Dim blnIsConverted As Boolean

Not there.

Declare it and see the difference!

You are declaring it within the if then statement, so it is declared if the conditions are met.
When you put this in a do loop it is not declared on a conditional basis.
Declare it outside the loop and have it available.

Peter Leow · Answer 2 · 2014-04-06T15:19:00

In For loop, it is 3-in-1:
1. declaration and initialization of

dblRate As Double = 0.05

2. condition check

dblRate <= 0.1

3. increase by dblRate by 0.01 for each iteration

In the case of Do While loop, it only checks the condition, i.e. point 2. You have to take care of points 1 and 3 separately in your code. See example:

VB

If blnIsConverted Then
     ' must declare and initilise dblRate
     Dim dblRate As Double = 0.05

     Do While dblRate <= 0.1
        ' other code
        ' increase by the step value of 0.01
        dblRate = dblRate  + 0.01
     Loop

Next dblRate

How do I change this For... Next statementinto a Do...Loop

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