1 /* 2  *atoi() 3  * 4  * To convert a string to integer 5  *  6  */ 7 #include
     
       8 #include
      
        9 #define IS_DIGIT(_arg_) ({char _ch_ = _arg_ ;(_ch_ >= '0'&&_ch_ <= '9');})10 int my_atoi(const char *str);11 12 int main(int argc, const char *argv[])13 {14     int value;15     value = my_atoi("-123456");16     printf("value:%d\n",value);17     18     return 0;19 }20 21 int my_atoi(const char *str)22 {23     int integer = 0;24     const char *p = str;25     int flag = 1;26     switch(*p)27     {28     case '+':29         p++;30         break;31     case '-':32         flag = -1;33         p++;34         break;35     default:36         break;37     }38 39     for(;'\0' != *p && IS_DIGIT(*p);p++)40     {41         integer *= 10;42         integer += *p - '0';43     }44 45     return flag > 0 ? integer : -integer;46 47 }