Compilare: user.cpp: In function ‘int main()’: user.cpp:56:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<gr[i].size();j++) ^ user.cpp: In function ‘char nextch()’: user.cpp:13:36: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(buf, BUF_SIZE, 1, fi); ^