将×××字符串转换为×××，不适用预定的函数

算法：    
class StrToInt
             {
                /********************************************************
                 *    
                 *            程序名称:将字符串转换为×××
                 *    
                 *            作     者：李吉忠
                 *            
                 *            主要算法: TransToInt(string str)
                 *            说     明:    如果输入的不是×××字符，如12ab37等将返回-1
                 *                             传入的参数为正常时返回为正确值
                 *            完成时间：2013-3-8
    
                 */
                static int TransToInt(string str)    
                {
                        char[] ch = str.ToCharArray();
                        int []nArray = new int[str.Length];
                        int nReturn = 0;
                        for (int i = 0; i < ch.Length; i++)
                        {
                                if (ch[i] - 48 < 0 || ch[i] - 48 > 9)
                                {
                                        return -1;
                                }
                                else    
                                {
                                        nArray[i] =ch[i]-48;

                                        nReturn += nArray[i] * (int)Math.Pow(10, ch.Length - 1 - i);
                                }
                        }
                        return nReturn;
                }
                static void Main(string[] args)
                {
                        Console.WriteLine(TransToInt("12345"));
                        Console.Read();
                }

}

运行结果：