Help: Using R from C

Hi folks:

I am just beginning to try and use R from my own C programs.  Platform is
Windows2000, compiler Visual C++ 6.0.  I built the import library R.lib from
R.dll using the VC LIB.exe program.  Here is a simple code I am trying to
compile and run (no C++, VC++ is instructed to treat it strictly as C):

#include "R.h"
#include "Rinternals.h"

int main(void)
{
	int i;
	char *greeting;
	SEXP x;

	greeting = (char *) Calloc(31, char);
	sprintf(greeting, "\nCallRFromC: test 1\n");
	printf(greeting);

	printf("Here is a vector:\n");

	/* allocate an R vector */
	PROTECT(x = allocVector(REALSXP, 10));
	for(i=0; i<10; i++) {
		REAL(x)[i] = (double)i;
		printf("  x[%2d] = %lf\n", REAL(x)[i]);
	}
	UNPROTECT(1);

	return 0;
}

The code builds without any problem (I am linking it with the import library
R.lib, and R.dll is in the path).  While running, though, the code segfaults at
the allocVector(...) call.  The error message is [The instruction at
"0x002ee77e" referenced memory at ")x0000000c". The memory could not be "read".
Click on OK to terminate the program]

Stepping into the code using the debug mode, the crash happens at the
allocVector(...) call.

Am I missing something obvious here?  Any help is greatly appreciated.