Compilare: main.cpp: In function 'void solve_prb()': main.cpp:217:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<c.length(); i++) ~^~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:228:14: warning: unused variable 'a' [-Wunused-variable] unsigned a=0; ^ main.cpp: In function 'type get_type(const string&)': main.cpp:52:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ main.cpp: In function 'operation get_operation(const string&)': main.cpp:104:1: warning: control reaches end of non-void function [-Wreturn-type] } ^