Dissapearing SDL Rects. How to update window with new additional shapes

Question

I'm trying to update the window with a new additional rect upon key pressing, but it keeps disappearing due to SDL_RenderClear. Is it recommended to remove SDL_RenderClear?

while (!quit) {
  while (SDL_PollEvent( & e) != 0) {
    if (e.type == SDL_QUIT)
      quit = true;
  }
  SDL_SetRenderDrawColor(gRenderer, 0xFF, 0xFF, 0xFF, 0xFF);
  SDL_RenderClear(gRenderer); //if i remove this line, the new rectangle will remain there

  SDL_Rect fillRect = {
    0,
    0,
    SCREEN_WIDTH / 5 - 5,
    SCREEN_HEIGHT / 5 - 5
  };
  SDL_SetRenderDrawColor(gRenderer, 255, 205, 51, 0xFF);
  SDL_RenderFillRect(gRenderer, & fillRect);

  switch (e.type) {
  case SDL_KEYDOWN:
    if (e.key.keysym.sym == SDLK_RIGHT) {
      SDL_Rect fillRect = {
        0,
        200,
        SCREEN_WIDTH / 5 - 5,
        SCREEN_HEIGHT / 5 - 5
      };
      SDL_SetRenderDrawColor(gRenderer, 255, 205, 51, 0xFF);
      SDL_RenderFillRect(gRenderer, & fillRect);
    }
    break;
  }
  SDL_RenderPresent(gRenderer);
}

Answer 1

SDL_RenderClear() is perfectly fine and in fact you should be using it. Your problem (aka the rect disappearing) is caused by the way you handle input. SDL_KEYDOWN is an event that only occurs on the frame that you press a key for, and while you're holding it down after a short delay. What you are doing is drawing the rect if the key has been pressed on that exact frame, not if it's been pressed on any previous frames. A solution via a bool could look like this:

bool keyPressed = false;
while( !quit ) {
    while( SDL_PollEvent( &e ) != 0 ) {
        if( e.type == SDL_QUIT )
            quit = true; 
}
    SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
    SDL_RenderClear( gRenderer ); //if i remove this line, the new rectangle will remain there

    SDL_Rect fillRect = { 0, 0, SCREEN_WIDTH / 5-5, SCREEN_HEIGHT / 5-5 };
    SDL_SetRenderDrawColor( gRenderer, 255, 205, 51, 0xFF );        
    SDL_RenderFillRect( gRenderer, &fillRect );
    
    if(keyPressed){
        SDL_Rect fillRect = { 0, 200, SCREEN_WIDTH / 5-5, SCREEN_HEIGHT / 5-5 };
        SDL_SetRenderDrawColor( gRenderer, 255, 205, 51, 0xFF );        
        SDL_RenderFillRect( gRenderer, &fillRect );
}
    switch(e.type){
    case SDL_KEYDOWN:
        if(e.key.keysym.sym==SDLK_RIGHT){
            keyPressed = true;
        }
  break;
 }
   SDL_RenderPresent( gRenderer );
}

Screen clearing is something that should absolutely be done in graphics, because otherwise the shapes you've drawn on previous frames will just remain there.