Simple SDL2 program to draw lines (left-click and drag to draw lines, right to erase)

line-draw.c

#include <SDL2/SDL.h>
#include <stdbool.h>

struct pt_pair {
  SDL_Point begin;
  SDL_Point end;
};

int main() {
  SDL_Init(SDL_INIT_AUDIO);
  SDL_Window *w;
  SDL_Renderer *r;

  SDL_CreateWindowAndRenderer(800, 600, 0, &w, &r);

  SDL_Event e;

  struct pt_pair *pt_pairs = NULL;
  int n_pts = 0;
  
  SDL_Point begin = {0};
  SDL_Point end = {0};
  
  bool dragging = 0;
  bool running = 1;

  while (running) {
    while (SDL_PollEvent(&e)) {
      switch (e.type) {
        case SDL_KEYDOWN:
          switch (e.key.keysym.sym) {
            case SDLK_ESCAPE:
              running = false;
            break;
          }
        break;

        case SDL_MOUSEBUTTONDOWN:
          if (e.button.button == SDL_BUTTON_LEFT)
          {
            dragging = 1;

            begin.x = end.x = e.button.x;
            begin.y = end.y = e.button.y;
          }
        break;

        case SDL_MOUSEBUTTONUP:
          if (e.button.button == SDL_BUTTON_LEFT) {
            dragging = 0;

            pt_pairs = realloc(pt_pairs, sizeof(struct pt_pair) * (n_pts + 1));
            
            pt_pairs[n_pts].begin = begin;
            pt_pairs[n_pts].end = end;

            ++n_pts;
          } else if (e.button.button == SDL_BUTTON_RIGHT) {
            n_pts = 0;
            // free(pt_pairs);
          }
        break;

        case SDL_MOUSEMOTION:
          if (dragging)
          {
            end.x = e.motion.x;
            end.y = e.motion.y;
          }
        break;

        case SDL_QUIT:
          running = false;
        break;
      }
    }

    SDL_SetRenderDrawColor(r, 0x0,  0x0,  0x0,  0xFF);
    SDL_RenderClear(r);
    SDL_SetRenderDrawColor(r, 0xFF, 0xFF, 0xFF, 0xFF);

    for (int i = 0; i < n_pts; ++i) {
      struct pt_pair pair = pt_pairs[i];
      
      SDL_RenderDrawLine(r, pair.begin.x, pair.begin.y, pair.end.x, pair.end.y);
    }

    if (dragging)
      SDL_RenderDrawLine(r, begin.x, begin.y, end.x, end.y);
    SDL_RenderPresent(r);
  }

  SDL_DestroyRenderer(r);
  SDL_DestroyWindow(w);
  SDL_Quit();
}