htoi的实现

htoi的实现

 /*************************************************************************
     > File Name: htoi.c
     > Author: ChenPeng
     > Mail:479103815@qq.com
     > Blog: http://www.cnblogs.com/cpsmile/
     > Created Time: Fri 03 Apr 2015 07:22:15 PM CST
  ************************************************************************/
 #include<stdio.h>
 #include<stdlib.h>
 
 #define YES 1
 #define NO 0
 
 /*将十六进制数字组成的字符串转换为与之等价的整型值*/
 int htoi(char *str)
 {
     int hexdigit;//记录每一个十六进制数对应的十进制数
     int i;//工作指针
     int ishex;//是否是有效的十六进制数
     int n;//返回的十进制数
 
     i= ;
     if(str[i] == '')
     {
         ++i;
         if(str[i] == 'x' || str[i] == 'X')
             ++i;
     }
     n = ;
     ishex = YES;
     for(; ishex == YES; ++i)
     {
         if(str[i] >= '' && str[i] <= '')
             hexdigit = str[i] - '';
         else if(str[i] >= 'a' && str[i] <= 'f')
             hexdigit = str[i] - 'a' + ;
         else if(str[i] >= 'A' && str[i] <= 'F')
             hexdigit = str[i] - 'A' + ;
         else
             ishex = NO;
         if(ishex == YES)
             n =  * n + hexdigit;
     }
     return n;
 }
 
 int main()
 {
     char str[] = "";
     int val;
     while(printf("Please enter a hex string:\n"),scanf("%s",str) == )
     {
         val = htoi(str);
         printf("整数是：%d\n",val);
     }
     return ;
 }