strcpy函数实现

法一：
        void strcpy(char *s,char *t)
        {
                int i = 0;
                while((s[i] = t[i]) != '\0')
                    i++;
        }
法二：
        void strcpy(char *s,char *t)
        {
                while((*s = *t) != '\0')
                 {
                        s++;
                        t++;
                  }
        }
法三：
        void strcpy(char *s,char *t)
        {
                while((*s++ = *t++) != '\0')
                        ;
        }
法四：
        void strcpy(chat *s,cahr *t)
        {
                while((*s++ = *t++))
                        ;
        }