Same struct in two .cpp files

//main.cpp

#include <iostream>
#include "next.hpp"

extern carro Carrao;

int main() {
    saida();
    std::cout << Carrao.rodas << std::endl;
    Carrao.rodas = 10;
    std::cout << Carrao.rodas << std::endl;
    saida();
    std::cout << Carrao.rodas << std::endl;
    system("pause");
    return 1;
}

//next.cpp

#include <iostream>
#include "next.hpp"

carro Carrao;

void saida() {
    Carrao.rodas = 5;
}

//next.hpp

#ifndef NEXT_HPP
#define NEXT_HPP
struct carro {
    int rodas;
    int portas;
};

void saida();
#endif