Compilare: user.cpp: In function ‘std::vector<char> add(std::vector<char>, std::vector<char>)’: user.cpp:19:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i < a.size()) ^ user.cpp:21:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i < b.size()) ^ user.cpp: In function ‘std::vector<char> dif(std::vector<char>, std::vector<char>)’: user.cpp:37:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i < a.size()) ^ user.cpp:39:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i < b.size()) ^ user.cpp: In function ‘int main()’: user.cpp:76:26: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(fi,"%s " ,str); ^