字符串转整数(C#)

using System;
using System.Collections.Generic;

namespace StrToInt_CS
{
    class Program
    {
        static void Main(string[] args)
        {
             string str = "";
             while (!String.IsNullOrEmpty(str = Console.ReadLine()))
             {
                 KeyValuePair<int, bool> ret = Program.StrToInt(str);
                 if (ret.Value)
                 {
                     Console.WriteLine("Number for {0} is {1}", str, ret.Key);
                 }
                 else
                 {
                     Console.WriteLine("The input {0} is invalid", str);
                 }
             }
        }

        public static KeyValuePair<int, bool> StrToInt(string s)
        {
            bool isMinus = false;
            bool isValid = false;
            int num = 0;
            int k = 0;

            // if contain leading space, then invalid
            if (s[k] == ‘ ‘)
            {
                new KeyValuePair<int, bool>(num, isValid);
            }

            // if contain operator
            if (s[k] == ‘-‘)
            {
                isMinus = true;
                k++;
            }
            if (k < s.Length && s[k] == ‘+‘)
            {
                isMinus = false;
                k++;
            } 

            int flag = isMinus ? -1 : 1;

            for (int i = k; i < s.Length; i++)
            {
                if (s[i] >= ‘0‘ && s[i] <= ‘9‘)
                {
                    try
                    {
                        // check number is not overflow
                        checked
                        {
                            num = num * 10 + flag * (s[i] - ‘0‘);
                        }
                    }
                    catch (Exception)
                    {
                        isValid = false;
                        break;
                    }
                }
                else
                {
                    break;
                }

                // if complete traverse the whole string, then is valid
                if (i + 1 == s.Length)
                {
                    isValid = true;
                }
            }

            return new KeyValuePair<int,bool>( num, isValid);
        }
    }
}

Test cases:

null

The input null is invalid

""

The input "" is invalid

" "

The input " " is invalid

The input    is invalid

123

Number for 123 is 123

+123

Number for +123 is 123

-123

Number for -123 is -123

1a3333

The input 1a3333 is invalid

+0

Number for +0 is 0

-0

Number for -0 is 0

2147483647

Number for 2147483647 is 2147483647

2147483648

The input 2147483648 is invalid

-2147483648

Number for -2147483648 is -2147483648

-2147483649

The input -2147483649 is invalid

+

The input + is invalid

-

The input - is invalid

++

The input ++ is invalid

__

The input __ is invalid

--

The input -- is invalid

字符串转整数(C#)