/in/foo.c: In function 'input':
/in/foo.c:26:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.c: In function 'left':
/in/foo.c:34:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.c: In function 'output':
/in/foo.c:41:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^