Why VS 2010 Express produces C2061 error on an old program that compiled successfully at one time with an old compiler?

I am not a C++ programmer, but I was assigned to compile an old program that was once compiled for a Unix  machine.  The program now needs to run in Windows.

When I try to compile the program in Visual Studio 2010 Express, I receive over 100 error messages.  The errors that mainly shows up is the C2061: syntax error: Identifier ....

I've provided a snippet of the code to illustrate the error:

The code start of as follows:



#include <stdio.h>
#include <malloc.h>
#include <stdlib.h>



// class and structure declarations

class PATIENT;         // a patient record
class RULE;            // a rule from the file of pretty rules
class LINK;            // a node in a rule tree
struct TRIPLE;         // a staging triple (dx category, stage, pflag)
class DXLINK;          // single dx link
class DXRLINK;         // dx range link
class STLINK;          // stage link
class XLINK;           // sex link
class WLINK;           // without clause link
struct STAGE;          // dxcat and stage
struct DXRANGE;        // lo and hi dxs


.....



The error message generates  for the above code lines are as follows:


1>------ Build started: Project: Stager, Configuration: Debug Win32 ------
1>  stager.C
1>s:\carmen\stager.c(15): error C2061: syntax error : identifier 'PATIENT'
1>s:\carmen\stager.c(15): error C2059: syntax error : ';'
1>s:\carmen\stager.c(16): error C2061: syntax error : identifier 'RULE'
1>s:\carmen\stager.c(16): error C2059: syntax error : ';'
1>s:\carmen\stager.c(17): error C2061: syntax error : identifier 'LINK'
1>s:\carmen\stager.c(17): error C2059: syntax error : ';'
1>s:\carmen\stager.c(19): error C2061: syntax error : identifier 'DXLINK'
1>s:\carmen\stager.c(19): error C2059: syntax error : ';'
1>s:\carmen\stager.c(20): error C2061: syntax error : identifier 'DXRLINK'
1>s:\carmen\stager.c(20): error C2059: syntax error : ';'
1>s:\carmen\stager.c(21): error C2061: syntax error : identifier 'STLINK'
1>s:\carmen\stager.c(21): error C2059: syntax error : ';'

...

=============


If anyone can help me with this error, I really would appreciate it so that I can move forward with the program.

Thank you for your assistance.