CODEWITHSUNDEEP
c#radixbase-conversion
doc_id
doc_id

Reputation: 1443

C# base converter

I stumbled on this method which should do a base convert from a 10 base to radix base, so for example if I pass 28, 16 it should return 1c which is the hexadecimal representation of the decimal 28

private static string convertTo(long value, int radix)
{
    char[] alphabet = "0123456789abcdefghijklmnopqrstuv".ToCharArray();
    string result = "";

    if (value < radix) {
        return alphabet[value].ToString();
    }

    long index;
    while (value != 0)
    {
        index = value % radix;
        value = Convert.ToInt64(Math.Floor(value / radix));  
        result += alphabet[index].ToString();
    }
    return result;
}

I'm rewriting that part of the program in PHP. By reading the code above, and predicting output manually, it returns c1 where it should return 1c for 28, 16

My finding is that this method returns a reversed representation of string in a given base, c1 instead of correctly 1c

Because I do not have a C# compiler I could not verify my findings.

So here are my two questions:

  1. Are my calculations right that the above method calld with 28, 16 returns c1?
  2. I suppose symbols (digits/alphabets), in any base, are written so that base exponents decreases by 1 as we go from left to write, so for example in decimal representation 312 means 300 (3 * 10 ^ 2) + 10 (1 * 10 ^ 1) + 2 (2 * 10 ^ 0).. is that absolutely always correct?

Upvotes: 1

Views: 2533

Answers (3)

Sake
Sake

Reputation: 150

  1. For me, yes. the snippet in C# (as it is) should return C1, instead of 1C. You will need to reverse the string result before returning it. (or use instead something like result = string.Concat(alphabet[index].toString()); when creating the result string)

  2. That's correct. It also works in all the other bases, i.e. if we take your example (28), you'll have :

28 = 2 * 10^1 + 8 * 10^0 (base 10)

28 = 1 * 16^1 + 12 * 16^0 (base 16) = 1C

28 = 3 * 8^1 + 2 * 8^0 (base 8) = 32

etc, etc.

Upvotes: 2

norlesh
norlesh

Reputation: 1861

Yes you are correct convertTo(28, 16) == c1 The loop in the code should be:

while (value != 0)
{
    index = value / radix; // implicit integer division  
    value = value % radix;
    result += alphabet[index].ToString();
}

As to your second question I believe that to be correct also - that's more for a mathematics expert to verify though.

Upvotes: 1

Kory Gill
Kory Gill

Reputation: 7163

Yes, that code needs to reverse the output. Below are the results when I ran that code in Visual Studio 2015, and the corresponding output in the Locals window.

    var ret1 = convertTo(28, 16);
    var ret2 = convertTo(28, 10);
    var ret3 = convertTo(10, 10);

    ret1    "c1"    string
    ret2    "82"    string
    ret3    "01"    string

Upvotes: 1

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