1.cpp

#include "SDL.h"
#include "SDL_image.h"
#include <stdexcept>
#include <string>
#include <iostream>

2.cpp

const int SCREEN_WIDTH  = 640;
const int SCREEN_HEIGHT = 480;

SDL_Renderer *renderer = nullptr;
SDL_Window *window = nullptr;

3.cpp

SDL_Texture* LoadImage(std::string file){
    SDL_Texture* tex = nullptr;
    tex = IMG_LoadTexture(renderer, file.c_str());
    if (tex == nullptr)
        throw std::runtime_error("Failed to load image: " + file + IMG_GetError());
    return tex;
}

4.cpp

    SDL_Texture *background = nullptr, *image = nullptr;
    try {
        background = LoadImage("../res/Lesson3/background.png");
        image = LoadImage("../res/Lesson3/image.png");
    }
    catch (const std::runtime_error &e){
        std::cout << e.what() << std::endl;
	return 4;
    }