Compilare: user.cpp: In function ‘void Solve()’: user.cpp:24:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i <= str.size()) { ^ user.cpp:28:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i<str.size() && '0' <= str[i] && str[i] <= '9') { ^ user.cpp:46:62: warning: array subscript has type ‘char’ [-Wchar-subscripts] while(o > 0 && op[o] != '(' && pr[op[o]] >= pr[ch]) { ^ user.cpp: In function ‘int Operation(int, int, int)’: user.cpp:81:1: warning: control reaches end of non-void function [-Wreturn-type] } ^