Rounding a number down in Visual Basic

vb.net math rounding

55,420

Solution 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

Solution 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

Solution 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

-- Furry cows moo and decompress.

Solution 4

To round down

Math.Floor(number)

To trim characters

number.Substring(0,1)

You can convert it to string.

Solution 5

Dim Input As Decimal
Dim Output As Decimal
Input = 2.556
Output = Input - (Input Mod 0.01)

This will work with both positive and negative numbers

View more solutions

55,420

Author by

Paul

@PaulKinrossGray

Updated on July 09, 2022

Comments

Paul almost 2 years
I have a Visual Basic application that needs to round a number down, for example, 2.556 would become 2.55 and not 2.26.

I can do this using a function to strip off the characters more than 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)
```
Is there a better function to do this?
Justin almost 15 years

Using Fix() will be slightly faster than using Floor().
Reed Copsey almost 15 years

Do you anything that supports that statement?
Shvalb almost 15 years

Sometimes it's beneficial to store your numbers as integers, or fixed-point (if you don't need the full range of floating-point), performing calculations on the fixed-point numbers and then adjust them when displaying to the user.
Reed Copsey almost 15 years

@Justin: Good point - I edited to account for negative numbers, as well as positive
Reed Copsey almost 15 years

@Justin: Fix is actually slower than Math.Floor - it does a check, then calls Math.Floor internally. Run reflector on Microsoft.VisualBasic.dll for details.
Saul Dolgin almost 15 years

I am used to the Fix() function from VB6, but it is available in VB.NET as well - msdn.microsoft.com/en-us/library/…
Reed Copsey almost 15 years

@WyrdestGeek: The function is Math.Sign. @Saul: Fix calls Math.Floor internally.
Saul Dolgin almost 15 years

What is this business about decompressing bovines?
Justin almost 15 years

Whoops I said it backwards. Your comment was my rationale.
Robert L over 14 years

Since this is VB, just use a Currency datatype.