Math.Truncate

Consider a number like 1.234. It has an integral part—the value 1—and also a fractional part. With Math.Truncate we eliminate the fractional part.

For negative numbers, Math.Truncate also just removes the fractional part. This is different from the behavior of Math.Round, Ceiling, or Floor.

An example program

Here we introduce four Doubles and then call Math.Truncate on them. Their fractional parts are removed—their signs and integral parts are kept.

Module Module1

    Sub Main()
        Dim value1 As Double = 1.234
        Dim value2 As Double = 1.999
        Dim value3 As Double = -1.999
        Dim value4 As Double = -1.234

        Console.WriteLine(":::TRUNCATE:::")
        ' Use Math.Truncate to truncate the double values.
        Console.WriteLine(Math.Truncate(value1))
        Console.WriteLine(Math.Truncate(value2))
        Console.WriteLine(Math.Truncate(value3))
        Console.WriteLine(Math.Truncate(value4))

        Console.WriteLine(":::CAST:::")
        ' Use implicit Integer casts to truncate the double values.
        Dim value1Cast As Integer = value1
        Dim value2Cast As Integer = value2
        Dim value3Cast As Integer = value3
        Dim value4Cast As Integer = value4
        Console.WriteLine(value1Cast)
        Console.WriteLine(value2Cast)
        Console.WriteLine(value3Cast)
        Console.WriteLine(value4Cast)
    End Sub

End Module
:::TRUNCATE:::
1
1
-1
-1
:::CAST:::
1
2
-2
-1

Some notes

If a program uses smaller numbers only, then casting to Integer is acceptable and may be more efficient. But for large numbers, this can cause an overflow.

Like Math.Round, Ceiling and Floor, Math.Truncate changes the fractional part of a number. Its affects negative numbers in the same way as positive numbers.