I have a rand function that I defined in the rand.cpp file which I have
included in my program.  I don't have any problem with complie, however, it
always comes back with link errors:

ompiling...
simulation1.cpp
RAND.CPP
Linking...

defined in simulation1.obj

already defined in simulation1.obj

already defined in simulation1.obj
Debug/simulation1.exe : fatal error LNK1169: one or more multiply defined
symbols found
Error executing link.exe.

Here is part of my program:

#include <iostream.h>
#include <math.h>
#include "c:\rand.cpp"

int main()
{
 int i = 1;
 double number1;
 number1 = rand(i);
 cout << number1;
 return 0;

Besides, it should be .c not .cpp since the latter is typically used for
C++ source files. Since this is comp.lang.c and not comp.lang.c++ we
should stick with .c files.