Compilare: user.cpp: In function ‘void delete_spaces(char*)’: user.cpp:30:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for( i=0;i<strlen(c);i++) ^ user.cpp: In function ‘void extract_header(FILE*, FILE*)’: user.cpp:103:24: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(c,1025,f); ^ user.cpp: In function ‘void extract_columns(FILE*, FILE*)’: user.cpp:135:24: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(c,1025,f); ^