foo.cc: In function 'int main()':
foo.cc:8:12: warning: comparison of constant '100' with boolean expression is always true [-Wbool-compare]
  while (1<x<100)
         ~~~^~~~
foo.cc:8:10: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
  while (1<x<100)
         ~^~
foo.cc:10:9: error: lvalue required as left operand of assignment
  if(x%2=0)
         ^
foo.cc:13:8: error: unable to find numeric literal operator 'operator""x'
  cout<<3x+1<<endl;
        ^~
foo.cc:13:8: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes