Subtle differences from VB and C

Posted on 3 mins read

For those who works like me with both languages, sometimes we can encounter some subtle differences between VB and C#. Take this code in VB

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Module Module1

    Private Function NormalizeRank(ByVal userRank As Integer) As Integer
        Return CType(Math.Ceiling(Math.Min(userRank / 20, 5.0)), Integer)
    End Function

    Sub Main()

        For value As Integer = 0 To 101
            Console.WriteLine("{0} normalized is {1}", value, NormalizeRank(value))
        Next

    End Sub

End Module

Is a very stupid piece of code that is supposed to take a value in the range 0..100 and normalize in the new interval [0..5], if the user pass a value higher than 100 the result must be 5. We expect value from 1 to 20 to be transformed into 1, values from 21 to 40 to be transformed to 2 and so on. If you run this code you find that the result is expected one. Now suppose you need to translate this function to C#, probably the first thing you can write is this one.

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private static Int32 Normalize(Int32 rank)
{
    return (Int32)Math.Ceiling(Math.Min(rank / 20, 5.0));
}

static void Main(string[] args)
{
    for (int value = 0; value < 101; value++)
    {
        Console.WriteLine("{0} normalized is {1}", value, Normalize(value));
    }
}

If you think that this is correct, try to run the code, and find this result.

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0 normalized is 0
1 normalized is 0
2 normalized is 0
3 normalized is 0
4 normalized is 0
5 normalized is 0
6 normalized is 0
7 normalized is 0
8 normalized is 0
9 normalized is 0
10 normalized is 0
11 normalized is 0
12 normalized is 0
13 normalized is 0
14 normalized is 0
15 normalized is 0
16 normalized is 0
17 normalized is 0
18 normalized is 0
19 normalized is 0
20 normalized is 1
21 normalized is 1
22 normalized is 1
23 normalized is 1
24 normalized is 1

If you wonder why the normalization of a number like 2 is zero you need to think to the meaning of the operator / in both languages. In Visual Basic it means Floating point division while in C# the type of the operation is determined by the operands. so *2 / 20 in vb is 0.1 while 2 / 20 in C# is 0.*To solve this problem you need to write something like this

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private static Int32 Normalize(Int32 rank)
{
    return (Int32)Math.Ceiling(Math.Min(rank / 20.0, 5.0));
}

Now since 20.0 is a double, the compiler will emit a floating point division.

Alk.

Tags: C#