Compilare: main.c: In function 'main': main.c:17:9: warning: argument 2 null where non-null expected [-Wnonnull] 17 | fprintf(output, 0); | ^~~~~~~ In file included from main.c:1: /usr/include/stdio.h:350:12: note: in a call to function 'fprintf' declared 'nonnull' 350 | extern int fprintf (FILE *__restrict __stream, | ^~~~~~~ main.c:9:9: warning: variable 're' set but not used [-Wunused-but-set-variable] 9 | int re; | ^~ main.c:17:9: warning: null format string [-Wformat-overflow=] 17 | fprintf(output, 0); | ^~~~~~~~~~~~~~~~~~ main.c:10:14: warning: 'r' may be used uninitialized [-Wmaybe-uninitialized] 10 | while (b > 0) | ~~^~~ main.c:7:15: note: 'r' was declared here 7 | int a, b, r; | ^