Rounding a number down in VB

Question

Hi

I have a vb application that need to round a number down e.g. 2.556 would become 2.55 and not 2.26

I can do this using a function to strip off the characters more that 2 right from the decimal point using this:

Dim TheString As String
TheString = 2.556
Dim thelength = Len(TheString)
Dim thedecimal = InStr(TheString, ".", CompareMethod.Text)
Dim Characters = thelength - (thelength - thedecimal - 2)
_2DPRoundedDown = Left(TheString, Characters)

Does any one know of a better function to do this?

Answer 1

You can do this with Math.Floor. However, you'll need to multiply * 100 and divide, since you can't supply a number of digits

Dim theNumber as Double
theNumber = 2.556
Dim theRounded = Math.Sign(theNumber) * Math.Floor(Math.Abs(theNumber) * 100) / 100.0

Answer 2

Another way to do it that doesn't rely on using the String type:

Dim numberToRound As Decimal
Dim truncatedResult As Decimal
numberToRound = 2.556
truncatedResult = (Fix(numberToRound*100))/100

Answer 3

The Math.Floor( ) answer is good. I'm not sure exactly which VB environments Fix( ) is defined in. As Justin points out, Math.Floor( ) won't work with negative numbers. You'd have to take the absolute value, then multiply by the SGN( ) of the number. I don't know the exact name of the function that you'd use to get the SiGN (not sin() ) of the number.

In pseudo-code, taking negative values into account, the result would looks like:

result = sgn( num ) * floor( abs( num * RoundToDig ) ) / RoundToDig

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