How Would I add a constructor to this code. - c++

Question

Hey I am trying to make this space game. Now I have developed my ship, and am able to display it. However I would like to be able to use the class for more than one object. I can do this with a constructor but have no clue how to get a constructor working, what changes would I need to make to my code to make the object take an int value as a constructor and allow me to make multiple ships with the code by calling the object.
Here is my header file.
//
// Ship.hpp
// Zerg_Invasion
//
// Created by Flik Wolf on 11/9/15.
//
//
#ifndef Ship_h
#define Ship_h
#include <stdio.h>
#include "ofMain.h"
class Ship {
public:
// Constructor
Ship();
// Methods
void moveLeft();
void moveRight();
void load();
void draw();
void fire();
void keyPressed();
// Properties
int x;
int y;
ofColor color;
ofImage cat;
};
#endif
and here is my CPP file.
//
// Ship.cpp
// Zerg_Invasion
//
// Created by Flik Wolf on 11/9/15.
//
//
#include "Ship.h"
Ship::Ship() {
// Set the initial color
//color.set( ofRandom(255), ofRandom(255), ofRandom(255));
// Initial x position of the ball
x = 450;
// Initial y position of the ball
y = 200;
}
void Ship::moveLeft() {
x -= 10;
}
void Ship::moveRight() {
x += 10;
}
void Ship::load() {
cat.load("spaceShip.png");
}
void Ship::draw() {
cat.draw(x, y);
// ofCircle(x, y, 30);
}
void Ship::fire() {
ofSetColor(255, 255, 255);
ofCircle(x, 200, 2);
}
Also here is the .h and .cpp files for Openframeworks which I am using for graphics.
#pragma once
#include "ofMain.h"
#include "Ship.h"
class ofApp : public ofBaseApp {
public:
void setup();
void update();
void draw();
void keyPressed(int key);
void keyReleased(int key);
void mouseMoved(int x, int y);
void mouseDragged(int x, int y, int button);
void mousePressed(int x, int y, int button);
void mouseReleased(int x, int y, int button);
void mouseEntered(int x, int y);
void mouseExited(int x, int y);
void windowResized(int w, int h);
void dragEvent(ofDragInfo dragInfo);
void gotMessage(ofMessage msg);
Ship theShip;
};
#include "ofApp.h"
//--------------------------------------------------------------
void ofApp::setup() {
// Smooth edges
ofEnableSmoothing();
// Fixed framerate
ofSetFrameRate(120);
theShip.load();
// No need to define the initial position of the ball
// because the Ball constructor does it for you
}
//--------------------------------------------------------------
void ofApp::update() {
// theShip.move();
}
//--------------------------------------------------------------
void ofApp::draw() {
ofBackground(0);
std::vector <int> nums;
nums.push_back(0);
nums.push_back(1);
nums.push_back(3);
nums.push_back(4);
nums.push_back(5);
nums.push_back(6);
nums.push_back(7);
nums.push_back(8);
cout << nums[0] << endl;
cout << nums[1] << endl;
theShip.draw();
}
//--------------------------------------------------------------
void ofApp::keyPressed(int key) {
if (key == 'a')
{
theShip.moveLeft();
}
if (key == 'd')
{
theShip.moveRight();
}
}
//--------------------------------------------------------------
void ofApp::keyReleased(int key) {
}
//--------------------------------------------------------------
void ofApp::mouseMoved(int x, int y) {
}
//--------------------------------------------------------------
void ofApp::mouseDragged(int x, int y, int button) {
}
//--------------------------------------------------------------
void ofApp::mousePressed(int x, int y, int button) {
theShip.fire();
}
//--------------------------------------------------------------
void ofApp::mouseReleased(int x, int y, int button) {
}
//--------------------------------------------------------------
void ofApp::mouseEntered(int x, int y) {
}
//--------------------------------------------------------------
void ofApp::mouseExited(int x, int y) {
}
//--------------------------------------------------------------
void ofApp::windowResized(int w, int h) {
}
//--------------------------------------------------------------
void ofApp::gotMessage(ofMessage msg) {
}
//--------------------------------------------------------------
void ofApp::dragEvent(ofDragInfo dragInfo) {
}

Answer 1

As mentioned, the constructor in your case should only produce one ship, and this should be the case with all object constructors.
However, it's still easy enough to create and maintain multiple ships (as you've implemented them) if you use a container like std::vector.
Containing multiple ships:
To create a container for your ships, you can use a vector like so:
std::vector<Ship> Ships;
Adding new ships:
To add additional ships to it, you can use std::vector::push_back():
Ships.push_back(Ship()); //Adds a new ship to 'Ships'
Updating the ships:
There are a couple of ways to cycle through your ships:
for (auto& i : Ships)
i.Update(); //Some updating function for each ship
Or, if you need to keep track of the specific position of each ship inside the vector:
for (unsigned int i = 0; i < Ships.size(); ++i)
Ships[i].Update() //The same updating function

Answer 2

How about to get the x and y as constructor argument?
in the .h file:
struct Ship {
// Constructor
Ship(int _x = 450, int _y = 200);
// ...
in the cpp file:
Ship::Ship(int _x, int _y) : x{_x}, y{_y} {
// Set the initial color
//color.set( ofRandom(255), ofRandom(255), ofRandom(255));
}