In file included from /usr/include/c++/3.2.2/backward/iostream.h:31, from grad.cpp:1: /usr/include/c++/3.2.2/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header. Please consider using one of the 32 headers found in section 17.4.1.2 of the C++ standard. Examples include substituting the <X> header for the <X.h> header for C++ includes, or <sstream> instead of the deprecated header <strstream.h>. To disable this warning use -Wno-deprecated. grad.cpp: In function `int main()': grad.cpp:19: warning: NULL used in arithmetic grad.cpp:26: warning: value computed is not used grad.cpp:39: warning: value computed is not used /tmp/ccizeh9r.o(.text+0x4f): In function `main': : the `gets' function is dangerous and should not be used.