Compilare: user.cpp: In function ‘int main()’: user.cpp:46:32: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘std::vector<std::vector<int> >::size_type {aka long unsigned int}’ [-Wformat=] fprintf(fo,"%d\n", M.size()); ^ user.cpp:47:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < M.size(); i++){ ^ user.cpp:48:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < M[i].size(); j++) fprintf(fo,"%d ", M[i][j]); ^ user.cpp:39:30: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(fi,"%d%d", &n, &m); ^ user.cpp:41:34: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(fi,"%d%d", &a, &b); ^