易百教程

using System;

class Program {
   static void Main() {
      string str = "1001";
      Console.WriteLine("Integer:"+ConvertClass.Convert(str));
   }
}

public static class ConvertClass {
   public static int Convert(string str1) {
      if (str1 == "")
         throw new Exception("Invalid input");
      int val = 0, res = 0;

      for (int i = 0; i < str1.Length; i++) {
         try {
            val = Int32.Parse(str1[i].ToString());
            if (val == 1)
               res += (int)Math.Pow(2, str1.Length - 1 - i);
            else if (val > 1)
               throw new Exception("Invalid!");
         } catch {
            throw new Exception("Invalid!");
         }
      }
      return res;
   }
}