#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <iostream>
#include <cmath>

const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int FPS = 60;
const double PI = 3.141592653589793;

// Structure to store the position and velocity of an object
struct Vector2D
{
    double x, y;
    double dx, dy;
};

// Calculate the distance between two vectors
double distance(Vector2D v1, Vector2D v2)
{
    return sqrt(pow(v1.x - v2.x, 2) + pow(v1.y - v2.y, 2));
}

int main(int argc, char* argv[])
{
    // Initialize SDL
    SDL_Init(SDL_INIT_VIDEO);

    // Create a window and renderer
    SDL_Window* window = SDL_CreateWindow("Earth Animation", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);

    // Load the Earth texture
    SDL_Surface* surface = IMG_Load("earth.png");
    SDL_Texture* texture = SDL_CreateTextureFromSurface(renderer, surface);
    SDL_FreeSurface(surface);

    // Create a vector for the Earth's position and velocity
    Vector2D earth;
    earth.x = SCREEN_WIDTH / 2;
    earth.y = SCREEN_HEIGHT / 2;
    earth.dx = 0;
    earth.dy = -200;

    // Create a vector for the Moon's position and velocity
    Vector2D moon;
    moon.x = SCREEN_WIDTH / 2;
    moon.y = SCREEN_HEIGHT / 2 - 200;
    moon.dx = 0;
    moon.dy = -250;

    // Set up the game loop
    bool quit = false;
    SDL_Event event;
    Uint32 startTime, endTime, deltaTime, delayTime;
    startTime = SDL_GetTicks();

    while (!quit)
    {
        // Handle events
        while (SDL_PollEvent(&event))
        {
            if (event.type == SDL_QUIT)
            {
                quit = true;
            }
        }

        // Calculate the deltaTime
        endTime = SDL_GetTicks();
        deltaTime = endTime - startTime;

        // Move the Earth and Moon
        earth.x += earth.dx * (deltaTime / 1000.0);
        earth.y += earth.dy * (deltaTime / 1000.0);
        moon.x += moon.dx * (deltaTime / 1000.0);
        moon.y += moon.dy * (deltaTime / 1000.0);

        // Calculate the angle between the Earth and Moon
        double angle = atan2(earth.y - moon.y, earth.x - moon.x);

        // Move the Moon in a circular orbit around the Earth
        moon.x = earth.x + cos(angle) * distance(earth, moon);
        moon.y = earth.y + sin(angle) * distance(earth, moon);

        // Clear the renderer
        SDL_RenderClear(renderer);

        // Render the Earth and Moon
        SDL_Rect earthRect = { (int)(earth.x - 64), (int)(earth.y - 64), 128, 128 };
        SDL_Rect moonRect = { (int)(moon.x - 32), (int)(moon.y - 32), 64, 64 };
        SDL_RenderCopy(renderer, texture, NULL, &earthRect);
        SDL_RenderCopy(renderer, texture, NULL, &moon

C++ Online Compiler

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Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}