foo.cc: In function 'int main()':
foo.cc:10:9: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
     if(d<c<a)
        ~^~
foo.cc:5:9: warning: variable 'b' set but not used [-Wunused-but-set-variable]
   int a,b,c,d;
         ^

[Hydro](https://hydro.ac)提供评测服务