foo.cc: In function 'int comp(char*)':
foo.cc:8:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i<=strlen(s)-2)
        ~^~~~~~~~~~~~~
foo.cc:12:17: warning: operation on 'top' may be undefined [-Wsequence-point]
    case'+': abc[--top]+=abc[top+1]; break;
                 ^~~~~
foo.cc:13:17: warning: operation on 'top' may be undefined [-Wsequence-point]
    case'-': abc[--top]-=abc[top+1]; break;
                 ^~~~~
foo.cc:14:17: warning: operation on 'top' may be undefined [-Wsequence-point]
    case'*': abc[--top]*=abc[top+1]; break;
                 ^~~~~
foo.cc:15:17: warning: operation on 'top' may be undefined [-Wsequence-point]
    case'/': abc[--top]/=abc[top+1]; break;
                 ^~~~~
foo.cc:7:18: warning: unused variable 'y' [-Wunused-variable]
  int i=0,top=0,x,y;
                  ^
foo.cc: In function 'int main()':
foo.cc:25:8: warning: 'char* gets(char*)' is deprecated [-Wdeprecated-declarations]
  gets(s);
        ^
In file included from /usr/include/stdio.h:862:0,
                 from /usr/include/c++/7/cstdio:42,
                 from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:46,
                 from foo.cc:1:
/usr/include/x86_64-linux-gnu/bits/stdio2.h:232:1: note: declared here
 gets (char *__str)
 ^~~~
foo.cc:25:6: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result [-Wunused-result]
  gets(s);
  ~~~~^~~
/tmp/ccGN5Sis.o: In function `main':
foo.cc:(.text.startup+0x11): warning: the `gets' function is dangerous and should not be used.

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。