foo.c:34:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
   34 | void main()
      |      ^~~~
foo.c: In function ‘yueshu’:
foo.c:24:9: warning: control reaches end of non-void function [-Wreturn-type]
   24 |         }
      |         ^
foo.c: In function ‘beishu’:
foo.c:33:9: warning: control reaches end of non-void function [-Wreturn-type]
   33 |         }
      |         ^