"how to convert a double value to char*?

double d_num;
char *ch_ptr;

ch_ptr = (char *)(&d_num);

Always ask correct question if need with propper suggestion."

Well I'm sorry Oleg, but if you're going to be pedantic:

You have cast a 'pointer to double' to a 'pointer to char' which is neither a literal interpretation of the OP's question nor a useful one, merely a wrong one.