Compilare: user.cpp: In function ‘int main()’: user.cpp:38:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while( i < expr.size() ) ^ user.cpp:120:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < postfix.size(); ++i ) ^ user.cpp:130:17: warning: ‘res’ may be used uninitialized in this function [-Wmaybe-uninitialized] int res; ^