How do I display the years correctly in my vb.net coding?

Question

I'm a beginner at using visual basic and I'm having trouble displaying my years correctly in my application. My application should display Rates: 3% - 7%, then under each rate Years should display: 1-5 and Balance should display a total amount per year. What I'm getting is 3% rate, years 1-5, and balance for each year. 4% rate is getting year 6, instead of 1-5 and balance for year six. 5% Rate is displaying year 7 and balance for that year, and so on. FYI: I need to keep the For...Next statement and incorporate a Do...Loop statement for "Years."

I inserted pics for a better understanding of what I'm trying to explain. I'd appreciate any help.

Correct Way Incorrect Way

Here is the code:

    Dim dblDeposit As Double
    Dim dblBalance As Double
    Dim intYear As Integer = 1

    Double.TryParse(txtDeposit.Text, dblDeposit)

    txtBalance.Text = "Rate" & ControlChars.Tab &
        "Year" & ControlChars.Tab & "Balance" &
        ControlChars.NewLine

    ' Calculate and display account balances. 
    For dblRate As Double = 0.03 To 0.07 Step 0.01
        txtBalance.Text = txtBalance.Text &
            dblRate.ToString("P0") & ControlChars.NewLine

        Do
            dblBalance = dblDeposit * (1 + dblRate) ^ intYear
            txtBalance.Text = txtBalance.Text &
                ControlChars.Tab & intYear.ToString &
                ControlChars.Tab & dblBalance.ToString("C2") &
                ControlChars.NewLine
            intYear = intYear + 1
        Loop While intYear < 6

    Next dblRate

Dai · Answer 1 · 2019-11-16T01:59:44.547

You need to reset intYear before each iteration of the Do loop.

    Dim dblDeposit As Double
    Dim dblBalance As Double
    Dim intYear As Integer = 1

    Double.TryParse(txtDeposit.Text, dblDeposit)

    txtBalance.Text = "Rate" & ControlChars.Tab &
        "Year" & ControlChars.Tab & "Balance" &
        ControlChars.NewLine

    ' Calculate and display account balances. 
    For dblRate As Double = 0.03 To 0.07 Step 0.01
        txtBalance.Text = txtBalance.Text &
            dblRate.ToString("P0") & ControlChars.NewLine

        intYear = 1 ' Reset intYear here before each loop

        Do
            dblBalance = dblDeposit * (1 + dblRate) ^ intYear
            txtBalance.Text = txtBalance.Text &
                ControlChars.Tab & intYear.ToString &
                ControlChars.Tab & dblBalance.ToString("C2") &
                ControlChars.NewLine
            intYear = intYear + 1
        Loop While intYear < 6

    Next dblRate

Some other recommendations:

String concatenation in a loop is inefficient because of how String works in .NET (String is immutable, so every operation that changes a string causes a reallocation and a copy, this is a somewhat expensive operation), so I recommend you use a StringBuilder and only assign txtBalance.Text at the very end.
You need to abort if the user enters invalid input. Also use the built-in currency parser (NumberStyles.Currency)
Always use Decimal or integer pennies/cents when working with money. Never use IEEE-754 floating-point types (Single and Double) to represent money because they are imprecise.
Avoid using Hungarian Notation (prefixing variable names with an abbreviation of their type).

    Dim depositAmount As Decimal
    If Not Decimal.TryParse( txtDeposit.Text, NumberStyles.Currency, CultureInfo.CurrentCulture, depositAmount ) Then
        MsgBox( "Invalid input" ).
        Exit Sub
    End If
    Dim sb As New StringBuilder()
    sb.Append( "Rate    Year    Balance" ).AppendLine() ' Tab characters are embedded in the string literal.
    ' Calculate and display account balances. 
    For rate As Double = 0.03 To 0.07 Step 0.01
        sb.AppendFormat( "  {0:P0}", rate ).AppendLine();
        Dim year As Integer = 1 ' Reset intYear here before each loop
        Do
            Dim balance As Decimal = depositAmount * ( 1 + rate ) ^ year ' I think you should add extra parenthesis to make it clear which value the `^ year` is being applied to.
            sb.AppendFormat( "  {0:D}   {1:C2}", year, balance ).ToString()
            year = year + 1
        Loop While year < 6
    Next rate

    txtBalance.Text = sb.ToString()

How do I display the years correctly in my vb.net coding?

1 Answers1