C SDL Object movement flow - c

Question

I just started with SDL and made a small square moving around on a window.
I used DL_GetKeyboardState, and got it moving kind of smoothly. However, just when I start moving it one direction by holding down one key, it moves a bit, stops, then move like I want. This messes up the smoothness. My best guess is that it waits for a doubleclick from the mouse, but im not sure. Any suggestions?
The code:
#include <stdio.h>
#include <SDL.h>
int main(int argc, char * argv[])
{
SDL_Window *window;
SDL_Renderer *renderer;
SDL_Event event;
SDL_Init(SDL_INIT_VIDEO);
window = SDL_CreateWindow("Yelda!", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 1600, 1200, 0);
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
const Uint8 *state;
int run = 1;
int xpos=300;
int ypos=300;
int projectileYPos;
int projectileXPos;
int loop;
int lanceLength = 10;
while(run)
{
while(SDL_PollEvent(&event))
{
state=SDL_GetKeyboardState(NULL);
if(state[SDL_SCANCODE_ESCAPE])
run=0;
if(state[SDL_SCANCODE_W])
ypos-=10;
if(state[SDL_SCANCODE_S])
ypos+=10;
if(state[SDL_SCANCODE_A])
xpos-=10;
if(state[SDL_SCANCODE_D])
xpos+=10;
SDL_SetRenderDrawColor(renderer, 0, 0, 0, 255);
SDL_RenderClear(renderer);
SDL_SetRenderDrawColor(renderer, 255, 255, 255 ,255);
SDL_Rect rect = {xpos, ypos, 20, 20 };
SDL_RenderFillRect(renderer, &rect);
SDL_RenderPresent(renderer);
SDL_Delay(20);
}
}
SDL_DestroyWindow(window);
SDL_DestroyRenderer(renderer);
SDL_Quit();
return 0;
}

Answer 1

The SDL wiki says that you should use SDL_PumpEvents() to update the keyboard state array.
And indeed, if we
remove the while(SDL_PollEvent(&event)) loop (not its contents) as it's unneeded,
move state=SDL_GetKeyboardState(NULL); before the while(run) loop (the address of the array "will be valid for the whole lifetime of the application", so it always returns the same pointer), and
only call SDL_PumpEvents() inside the loop,
then the movement is smooth.