convert astronomically large numbers into human readable form in C/C++

My program prints out HUGE numbers - like 100363443, up to a trillion -- and it sort of hard to read them, so I would like to print any number in easy to read form.

right now I use

printf ("%10ld", number);

format

I would appreciate a resulting number using printf. Most of my code is c++ yet I don't want to introduce std::cout, as I already have printf

thanks