foo.c: In function 'main':
foo.c:12:3: error: 'ch' undeclared (first use in this function)
   ch=getchar();
   ^~
foo.c:12:3: note: each undeclared identifier is reported only once for each function it appears in
foo.c:5:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d\n",&n,&m);
  ^~~~~~~~~~~~~~~~~~~~~~

Found 10 testcases.
[Hydro](https://hydro.ac)提供评测服务