foo.cc: In function 'int main()':
foo.cc:8:9: warning: comparison of constant '100' with boolean expression is always true [-Wbool-compare]
  int(1<x<100);
      ~~~^~~~
foo.cc:8:7: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
  int(1<x<100);
      ~^~
foo.cc:8:2: warning: statement has no effect [-Wunused-value]
  int(1<x<100);
  ^~~~~~~~~~~~