やっぱこうだろJK。

#include <stdio.h>

int main(void)
{
puts(
" * \n"
" *** \n"
" ***** \n"
" ******* \n"
"*********\n"
" ******* \n"
" ***** \n"
" *** \n"
" * \n"
);
return 0;
}