undefined reference to 'nCr' - c

Question

I'm trying to compile my program to run on linux but it doesn't work because of this error.
I compile with gcc -ansi -pedantic -Wall -m64 -o formula formula.c nCr.s and the error i get is:
/tmp/ccnNz7Jr.o: In function `main':
formula.c:(.text+0xc1): undefined reference to `nCr'
collect2: ld returned 1 exit status
make: *** [build] Error 1
Here's the code from the file formula.c
#include <stdio.h>
#include <stdlib.h>
#include "nCr.h"
#include <time.h>
#include <sys/time.h>
int main(int argc, const char * argv[])
{
int x = 0;
int y;
int z;
struct timeval start, end;
if (argv[1][0] == '-' && argv[1][1] == 'h') {
printf("Usage: formula <positive integer>");
} else {
y = atoi(argv[1]);
gettimeofday(&start, NULL);
printf("(1 + x)^%i = 1+", y);
if (y == 0)
printf("0");
if (y > 12) {
printf("%s\n","Please enter a number 12 or below. Anything higher results in overflow, the answer you want is not the answer you will get.");
}
for (; x <= y; x++) {
z = nCr(y, x);
if (z == -1) {
printf("Multiplication overflow. \n");
return 1;
} else {
if (x != 0)
printf("%i x^%i ",z , x);
if (x != y && x != 0)
printf("+ ");
}
}
gettimeofday(&end, NULL);
}
printf("\n%ld microseconds\n", ((end.tv_sec * 1000000 + end.tv_usec)
- (start.tv_sec * 1000000 + start.tv_usec)));
return 0;
}
ncr.h
#ifndef _NCR_H_
#define _NCR_H_
extern int Factorial(int n);
extern int nCr(int n, int r);
#endif /* _NCR_H_ */
and there's an assembly file called nCr.s
.globl _factorial
_factorial:
Leh_func_begin2:
pushq %rbp
Ltmp3:
movq %rsp, %rbp
Ltmp4:
movl %edi, -4(%rbp)
movl $1, -16(%rbp)
movl $1, -20(%rbp)
jmp LBB2_2
LBB2_1:
movl -16(%rbp), %eax
movl -20(%rbp), %ecx
imull %ecx, %eax
movl %eax, -16(%rbp)
movl -20(%rbp), %eax
addl $1, %eax
movl %eax, -20(%rbp)
LBB2_2:
movl -20(%rbp), %eax
movl -4(%rbp), %ecx
cmpl %ecx, %eax
jle LBB2_1
movl -16(%rbp), %eax
movl %eax, -12(%rbp)
movl -12(%rbp), %eax
movl %eax, -8(%rbp)
movl -8(%rbp), %eax
popq %rbp
ret
.globl _nCr
_nCr:
Leh_func_begin1:
pushq %rbp
Ltmp0:
movq %rsp, %rbp
Ltmp1:
subq $32, %rsp
Ltmp2:
movl %edi, -4(%rbp)
movl %esi, -8(%rbp)
movl -4(%rbp), %eax
xorb %cl, %cl
movl %eax, %edi
movb %cl, %al
callq _factorial
movl %eax, %ecx
movl %ecx, -20(%rbp)
movl -4(%rbp), %ecx
movl -8(%rbp), %edx
subl %edx, %ecx
movl %ecx, -24(%rbp)
movl -8(%rbp), %ecx
xorb %dl, %dl
movl %ecx, %edi
movb %dl, %al
callq _factorial
movl %eax, %ecx
movl -24(%rbp), %edx
xorb %sil, %sil
movl %edx, %edi
movb %sil, %al
movl %ecx, -32(%rbp)
callq _factorial
movl %eax, %ecx
movl -32(%rbp), %esi
imull %ecx, %esi
movl %esi, -28(%rbp)
movl -20(%rbp), %ecx
movl -28(%rbp), %esi
movl %ecx, %eax
cltd
idivl %esi
movl %eax, %ecx
movl %ecx, -16(%rbp)
movl %ecx, -12(%rbp)
movl -12(%rbp), %eax
addq $32, %rsp
popq %rbp
ret
Any help is greatly appreciated, can't seem to figure out why it's not compiling. It compiles just fine on mac but I need to get it run on linux.

Answer 1

GCC is not able to find extern int Factorial(int n); and extern int nCr(int n, int r); definitions because they are called _factorial: and _nCr: in your asm file. Change those labels to match the decl and your code will compile.
I noticed that you have only one call of nCr in the main function, so I think it is better to change decls in your .h. So your nCr.h will be:
#ifndef _NCR_H_
#define _NCR_H_
extern int _factorial(int n);
extern int _nCr(int n, int r);
#endif /* _NCR_H_ */
And you have to call _nCr(...) at main.