Convert number from base-10 number system to any number system

Question

I wrote a small method for convert number from base-10 number system to any number system (code is not perfect but that is not the point). My question is if I get right single responsibility principle. Is 2nd approach better than 1st or 'charReplace' functionality is too small for creating own method ?

 public static string convertNumber(BigInteger num, int baseNum)
 {
 string symbols = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 if (baseNum < 2 || symbols.Length + 10 < baseNum)
 {
 throw new Exception;
 }
 var result = "";
 do
 {
 var partResult = (int)(num % baseNum);
 if (partResult >= 10)
 {
 result = result.Insert(0, symbols[partResult - 10].ToString());
 }
 else
 {
 result = result.Insert(0, partResult.ToString());
 }
 num /= baseNum;
 } while (num != 0);
 return result;
 }

vs.

 static readonly string Symbols = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 public static string convertNumber(BigInteger num, int baseNum)
 {
 if (baseNum < 2 || Symbols.Length + 10 < baseNum)
 {
 throw new Exception;
 }
 var result = "";
 do
 {
 var partResult = (int)(num % baseNum);
 result = result.Insert(0, charReplace(partResult));
 num /= baseNum;
 } while (num != 0);
 return result;
 }
 private static string charReplace(int number){
 if (number < 10){
 return number.ToString();
 }
 return Symbols[number - 10].ToString();
 }

• 200_success: Pedantic note: BigInteger is not exactly a "base-10" number. It is just abstractly a number. While it's true that BigInteger.Parse() and BigInteger.ToString() both work in base ten, the BigInteger itself isn't in any particular base.

Answer 1

I believe the 1st approach is good enough since it personally more readable.

Little suggestions

• I'd prefer to store the whole alphabet in the symbols string, instead of only letters. This could simplify the logic.
• You can calculate the resulting length of the output string and avoid string insertions.

Summarizing:

public static string ConvertNumber(BigInteger num, int baseNum)
{
 const string symbols = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
 if (baseNum < 2 || symbols.Length < baseNum)
 {
 throw new ArgumentOutOfRangeException(nameof(baseNum));
 }
 if (num < 0)
 {
 throw new ArgumentOutOfRangeException(nameof(num));
 }
 var resultLength = 1 + Math.Max((int)BigInteger.Log(num, baseNum), 0);
 var result = new char[resultLength];
 int index = resultLength - 1;
 do
 {
 result[index--] = symbols[(int)(num % baseNum)];
 num /= baseNum;
 } while (num != 0);
 return new string(result);
}

PS. It's recommended to name all classes and all methods in UpperCamelCase regardless of their publicity.

• GRO: Thank you. Can you explain why is there Math.Max() ?
• Dmitry: @GRO Because if (num == 0) the log is -Infinity.