foo.c: In function ‘main’:
foo.c:6:16: warning: zero-length gnu_printf format string [-Wformat-zero-length]
    6 |         printf("");
      |                ^~
foo.c:5:21: warning: variable ‘d’ set but not used [-Wunused-but-set-variable]
    5 |         int n,a,b,c,d,e,f;
      |                     ^
foo.c:5:13: warning: unused variable ‘n’ [-Wunused-variable]
    5 |         int n,a,b,c,d,e,f;
      |             ^