Eroare de compilare: user.cpp: In function ‘void make_system()’: user.cpp:28: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void do_gauss()’: user.cpp:48: error: ‘abs’ was not declared in this scope user.cpp: In function ‘int main()’: user.cpp:71: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:72: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result