I grabbed this when it was originally published, but somehow the file name I have is different from the one in this article. Mine is called "carol.c" and I just compiled and ran it on a modern system. The compiler spat out the following warnings:

gcc -o carol carol.c

carol.c:2:1: warning: return type defaults to ‘int’ [-Wimplicit-int]

    2 | main(t,_,a )

      | ^~~~

carol.c: In function ‘main’:

carol.c:2:1: warning: type of ‘t’ defaults to ‘int’ [-Wimplicit-int]

carol.c:2:1: warning: type of ‘_’ defaults to ‘int’ [-Wimplicit-int]