Compilare: user.cpp: In function ‘void calc(int&)’: user.cpp:19:10: warning: statement has no effect [-Wunused-value] for(f;f<s.size();++f) ^ user.cpp:19:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(f;f<s.size();++f) ^ user.cpp: In function ‘int main()’: user.cpp:76:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) ^ user.cpp:90:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) ^