英文句子中首字母转换为大写

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string str = "Hello    my dear friend.";
            str.Trim();
            char c = '\0';
            string newStr = string.Empty;
            for (int k = 0; k < str.Length; k++)
            {
                //ASCII表中大小写字母正好相隔32，在ASCII表中32表示' ' A=65 Z=90 a=97 z=122   
                c = str[k];
                if ((c >= 'a' && c <= 'z') || c == ' ')
                {
                    if (k == 0)
                        c -= ' ';

                    if (c == ' ')
                    {
                        newStr += c.ToString();
                        if (str[k + 1] != ' ')
                        {
                            c = str[k + 1];
                            c -= ' ';
                            k++;
                        }
                    }
                }
                newStr += c.ToString();
            }
            Console.WriteLine(newStr);
            Console.ReadLine();
        }
    }
}