using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static int addAndSoustractNumberFromAString(string ustr)

    {

        int result = 0;

​

        if(!string.IsNullOrEmpty(ustr))

        {

            string str = ustr.Trim();

​

            //Regexes

            System.Text.RegularExpressions.Regex valid_regex = new System.Text.RegularExpressions.Regex(@"([\+\-]\d+)");

            System.Text.RegularExpressions.Regex invalid_regex = new System.Text.RegularExpressions.Regex(@"[a-zA-Z]");

​

            //Handling errors

            if (invalid_regex.IsMatch(str) || !valid_regex.IsMatch(str) || !Char.IsDigit(str[str.Length - 1])) return 0;

            Console.WriteLine(str);

            if (Char.IsDigit(str[0])) str = "+" + str;

​

            Console.WriteLine(str);

            Console.WriteLine(valid_regex);

            //Load all numbers in a string array

            List<string> numbers = new List<string>(valid_regex.Split(str)).Where(x => !String.IsNullOrEmpty(x)).ToList();

            Console.WriteLine("Count : " + numbers.Count);

​

            //Cast string numbers to int + result calculation

            foreach (string number in numbers) {

                Console.WriteLine(number);

                if (!int.TryParse(number, out int n)) 

                    return 99;

                result += n;

            }

        }

​

        return result;

    }

    public static void Main()

    {

        Console.WriteLine("Result : " + addAndSoustractNumberFromAString("52-2+3"));

    }

}