foo.cc: In function 'int main()':
foo.cc:30:9: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
   if(sta=end-1){
      ~~~^~~~~~
foo.cc:9:12: warning: unused variable 't' [-Wunused-variable]
  int n,s,e,t,sta,end;
            ^
foo.cc:10:9: warning: unused variable 'ans' [-Wunused-variable]
  double ans,res=1;
         ^~~
foo.cc:51:11: warning: 'e' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<a[e]<<endl;
           ^
foo.cc:50:11: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<a[s]<<endl;
           ^

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