in C how can i use numbers in the fopen function file open mode?

Question

in fopen(filename,"r") instead of r how can i use numbers?

Answer 1

char my_r[] = {0x72, 0x00};
fopen(filename, my_r);

but why would you want to?

Answer 2

I am guessing that what you are asking of this
rather than use "r"/"w" etc, you want to use O_RDWR/O_WRONLY etc.
Those are flags which have numerical values specified in header files.
I am not sure you should be specifying those numbers at all... since different compilers may interpret them differently. You are better off using "r" etc or maybe O_RDWR at the most