/in/foo.cc: In function 'int main()':
/in/foo.cc:14:15: warning: comparison of constant '20' with boolean expression is always true [-Wbool-compare]
   else if(10<z<=20) cout << 10*z;
           ~~~~^~~~
/in/foo.cc:14:13: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
   else if(10<z<=20) cout << 10*z;
           ~~^~
/in/foo.cc:15:15: warning: comparison of constant '30' with boolean expression is always true [-Wbool-compare]
   else if(20<z<=30) cout << 15*z;
           ~~~~^~~~
/in/foo.cc:15:13: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
   else if(20<z<=30) cout << 15*z;
           ~~^~