Compilare: main.cpp: In function 'bool is_op(char)': main.cpp:39:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < o.size(); ++i ) ~~^~~~~~~~~~ main.cpp: In function 'bool Eval(std::__cxx11::string)': main.cpp:56:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < s.size(); ++i ) { ~~^~~~~~~~~~ main.cpp: In function 'bool Do()': main.cpp:136:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < s1.size(); ++i ) { ~~^~~~~~~~~~~ main.cpp:144:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( int i = 0; i < s2.size(); ++i ) { ~~^~~~~~~~~~~ main.cpp: In function 'bool Calc(bool, bool, char)': main.cpp:34:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ main.cpp: In function 'int Priority(char)': main.cpp:50:1: warning: control reaches end of non-void function [-Wreturn-type] } ^