/in/foo.c:2:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
/in/foo.c: In function 'main':
/in/foo.c:7:9: warning: 'return' with a value, in function returning void
  return 0;
         ^
/in/foo.c:2:6: note: declared here
 void main()
      ^~~~