Compilare: user.cpp: In function 'int eval(std::string)': user.cpp:20: warning: comparison between signed and unsigned integer expressions user.cpp:23: warning: comparison between signed and unsigned integer expressions user.cpp:29: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'int main()': user.cpp:52: warning: comparison between signed and unsigned integer expressions user.cpp:61: warning: comparison between signed and unsigned integer expressions /tmp/ccsY3Kvg.o: In function `main': user.cpp:(.text+0xc8b): warning: the `gets' function is dangerous and should not be used.