[Original writeup](https://bigpick.github.io/TodayILearned/articles/2020-04/wpictf_writeups#autograder)

Go to the given website, and see that it is an online c-code compiler.

Run the given sample code and see that it actually tries to compile code.

Take advantage of the pre-processor by trying to include a common flag file name, "flag.txt":

#include </home/ctf/flag.txt>

And then click the compile/submit button. It spits out the file contents as it's not valid c code, and we get the flag in the process. Note, the < and > are required for this specifc implementation.