[Dev-C++] Help Needed

I was trying to compile a small program when the following messages =
popped up in the "Compiler and Linker Output" window:

c:\windows\TEMP\cc16bbgb.o(.text+0x110):gradefv.cpp: undefined reference =
to `read(istream &, Student_info &)'
c:\windows\TEMP\cc16bbgb.o(.text+0x194):gradefv.cpp: undefined reference =
to `compare(Student_info const &, Student_info const &)'

c:\windows\TEMP\cc16bbgb.o(.text+0x2b5):gradefv.cpp: undefined reference =
to `grade(Student_info const &)'

The compilation was said to be successful though. But there was zero =
output.

By the way, I am learning C++ on my own by reading Accelerated C++ =
Practical Programming by Example by A. Koenig and B. Moo. This problem =
occurred when I attempted to compile the example program. I checked the =
authors' source code too and attempted to run theirs. Their program had =
the same problem. What could be the problem? Help will be appreciated.

jyz