Compile C++ and MASM together

Question

I'm doing an exercise of an online course about MASM, specifically a project that use both C++ and MASM. The code of the C++ file is this:

#include <stdlib.h>
#include <iostream>

extern "C" void reverser(int *y, const int *x,int n);

int main(){
    using std::cout;
    using std::endl;

    const int n = 10;
    int x[n], y[n];

    for(int i = 0; i < n; i++)
        x[i] = i;

    reverser(y, x, n);

    for(int i = 0x0 ; i < n; i++){
        printf("x: %5d     y: %5d", x[i], y[i]);
    }

    return 0;
}

The code of the MASM file is this:

.386
.model flat, c
.code

reverser    proc
            push ebp        
            mov ebp,esp
            push esi
            push edi        ; Function Prologue

            xor eax,eax
            mov edi,[ebp+8]
            mov esi,[ebp+12]
            mov ecx,[ebp+16]
            test ecx,ecx

            lea esi,[esi+ecx*4-4]
            pushfd
            std

@@:         lodsd
            mov [edi], eax
            add edi,4
            dec ecx
            jnz @B

            popfd
            mov eax,1

            pop edi
            pop esi
            pop ebp
            
            ret

reverser endp
         end

On the online course the person speaking compile it with no problem using Visual Studio but if I try to compile the cpp file using gcc I get an error:

undefined reference to 'reverser'

So I tryed to add

#include "reverser.asm"

to the code but then I get the errors:

reverser.asm:1:error: expected unqualified-id before numeric constant
reverser.asm:1:error: expected ',' or ';' before numeric constant
reverser.asm:9:error: 'Prologo' does not name a type
reverser.asm:21:error: stray '@' in program

So I have the following questions:

1. How can I fix this?
2. How I can compile on Windows the 2 files together using the command-line? Like using masm.exe and gcc.exe to compile.
3. Why on the course it compiled without any problem?

Thank you so much, have a nice day! :D