數字轉字串(number to string) 字串轉數字(string to number)

正確來說是 整數轉字串 字串轉整數
integer to string and string to integer
char *itoa(int value, char *buffer, int radix);
http://www.cplusplus.com/reference/clibrary/cstdlib/itoa.html
int atoi ( const char * str );
http://www.cplusplus.com/reference/clibrary/cstdlib/atoi.html