This console application shows how to convert Base 32 numbers to decimal.

Convert Base 32 to decimal

// Huge thanks to my friend Ben Andrews for writing a version of this in Java. Rewriting it in C# was a 
// walk in the park after your work.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Base32Convertor
{
    class Program
    {
        static void Main(string[] args)
        {
            int intBase = 0;
            Console.WriteLine("What is your base?");

            String strBase = Console.ReadLine();
            if (!int.TryParse(strBase, out intBase))
            {
                return;
            }

            Console.WriteLine("What is your number?");
            string inputString = Console.ReadLine().ToUpper();

            char[] word = inputString.ToCharArray();
            double result = 0;
            int digit_count = 0;

            for (int i = word.Length - 1; i > -1; i--, digit_count++)
            {
                int coefficient = char_to_int(word[i]);
                double base_mult = Math.Pow(intBase, digit_count);
                result += (coefficient * base_mult);
            }
            Console.WriteLine("Result is " + result + ".");
            Console.ReadLine();
        }

        public static int char_to_int(char c)
        {
            int intval = (int)c;
            int ret = 0;

            if ((intval >= 48) && (intval <= 57))
            {
                /* This is a number */
                ret = (int)(intval - 48);
            }
            else if ((intval >= 65) && (intval <= 90))
            {
                /* This is a letter */
                ret = (int)(intval - 55);
            }

            return ret;
        }
    }
}