Compilare: user.cpp: In function 'int eval(std::string)': user.cpp:19: warning: comparison between signed and unsigned integer expressions user.cpp:22: warning: comparison between signed and unsigned integer expressions user.cpp:28: warning: comparison between signed and unsigned integer expressions user.cpp: In function 'int main()': user.cpp:53: warning: comparison between signed and unsigned integer expressions user.cpp:62: warning: comparison between signed and unsigned integer expressions /tmp/ccPErzew.o: In function `main': user.cpp:(.text+0xcab): warning: the `gets' function is dangerous and should not be used.