using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace ConsoleApp16

{

    public class Program

    {

        public static void Main(string[] args)

        {

            var input = "JPR5AU75";

            Console.WriteLine(GetNumericValue(input,'R'));

            //Expected output=5

            Console.WriteLine(UpdateNumericValue(input, 'R', 7));

            //Expected output=JPR7AU75

​

            input = "PR2.9AU75";

            Console.WriteLine(GetNumericValue(input, 'R'));

            //Expected output=2.9

            Console.WriteLine(UpdateNumericValue(input, 'R', 3.5));

            //Expected output=PR3.5AU75

​

            input = "PKLR555AU75";

            Console.WriteLine(GetNumericValue(input, 'R'));

            //Expected output=555

            Console.WriteLine(UpdateNumericValue(input, 'R', 765));

            //Expected output=PKLR765AU75

            Console.ReadLine();

        }

            static string GetNumericValue(string input, char c)

        {

            int charIndex = input.IndexOf(c);

​

            StringBuilder sb = new StringBuilder();

            int decimalCount = 0;

​

            for (int i = charIndex + 1; i < input.Length; i++)

            {

                if (char.IsNumber(input[i]) || input[i] == '.')

                {

                    if (input[i] == '.') decimalCount++;

                    if (decimalCount > 1) break;

​

                    sb.Append(input[i]);

                }

                else break;

            }

            return sb.ToString();

        }

​

        static string UpdateNumericValue(string input, char c, double newVal)

        {  

            var numericValue = GetNumericValue(input, c);

            return input.Replace(c + numericValue, c + newVal.ToString());            

        }

    }

}