Ошибка "идентификатор не определен" при создании производного класса

#include <iostream>
//#include "unit.h"
 
using namespace std;
 
class machine {
public:
    char *model;
    double cost;
    machine();
    ~machine();
};
 
machine::machine() {
    char *s;
    cout << "enter the model: "; cin >> s;
    cout << "enter the cost: "; cin >> cost;
    int length = strlen(s);
    model = new char[length + 1];
    strcpy(model, s);
}
 
machine::~machine() {
    cout << "deleting " << endl;
    delete model;
}
 
class truck : public machine {
private:
    double capacity;
public:
    truck() :machine() {}
    void print();
};
 
truck::truck() {
    cout << "enter the capacity "; cin >> capacity;
}
 
void print() {
    cout << "model: " << model << endl;
    cout << "cost: " << cost << endl;
    cout << "capacity: " << capacity << endl;
 
}

void truck::print() {

truck();

truck::truck() : machine() {
  cout << "enter the capacity "; cin >> capacity;
}

class machine {
public:
    char *model;
    double cost;
    machine(char *ch){
        cout << "enter the cost: "; cin >> cost;
        int length = strlen(ch);
        model = new char[length + 1];
        strcpy(model, ch);
    }
    ~machine() {
        cout << "deleting " << endl;
        delete model;
    }
};
 
class truck : public machine {
private:
    double capacity;
    char *ch;
public:
    truck(char *ch) : machine(ch) {
        cout << "enter the capacity "; cin >> capacity;
    }
    void print() {
        cout << "model: " << model << endl;
        cout << "cost: " << cost << endl;
        cout << "capacity: " << capacity << endl;
    }
};
 
int main() {
    truck t("toyota");
    t.print();
    system("pause");
    return 0;
}