Compilare: user.cpp: In function ‘int main()’: user.cpp:29:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) ^ user.cpp:43:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); i++) ^ user.cpp:55:9: warning: unused variable ‘c’ [-Wunused-variable] int c = a + b; ^