exo 30.cs

using System;

public class Class1
{
    static void Main(string[] args)
    {
        string num1 = "12";
        string num2 = "198111";

        Console.WriteLine(findSum(num1, num2));
    }

    static string findSum(string str1, string str2)
    {
        if (str1.Length > str2.Length)
        {
            string t = str1;
            str1 = str2;
            str2 = t;
        }

        string str = "";

        int n1 = str1.Length, n2 = str2.Length;

        char[] ch = str1.ToCharArray();
        Array.Reverse(ch);
        str1 = new string(ch);
        char[] ch1 = str2.ToCharArray();
        Array.Reverse(ch1);
        str2 = new string(ch1);

        int carry = 0;
        for (int i = 0; i < n1; i++)
        {
            int sum = ((int)(str1[i] - '0') + (int)(str2[i] - '0') + carry);
            str += (char)(sum % 10 + '0');

            carry = sum / 10;
        }

        for (int i = n1; i < n2; i++)
        {
            int sum = ((int)(str2[i] - '0') + carry);
            str += (char)(sum % 10 + '0');
            carry = sum / 10;
        }

        if (carry > 0)
        {
            str += (char)(carry + '0');
        }

        char[] ch2 = str.ToCharArray();
        Array.Reverse(ch2);
        str = new string(ch2);

        return str;
    }
}