Demonstração das funções para lidar com eventos de teclado usando SDL 2 com um protótipo simples, os exemplos estão descritos nesta postagem: https://wldomiciano.com/sdl-2-como-lidar-com-eventos-unicos-do-teclado/

game.c

// Testado no MinGW64
// gcc -Wall -Wextra -Wpedantic -Wno-unused-parameter game.c `sdl2-config --cflags --libs`
#include <SDL.h>

SDL_Window* window;
SDL_Renderer* renderer;

SDL_bool quit = SDL_FALSE;

// A tecla está pressionada?
SDL_bool isKeyPressed(int key) {
    return SDL_GetKeyboardState(NULL) [key];
}

// Variável global
Uint8 keyStates[SDL_NUM_SCANCODES];

// Reinicia estados
void resetKeyStates() {
    for (size_t i = 0; i < SDL_NUM_SCANCODES; i++)
        keyStates[i] = 0;
}

// A tecla foi pressinada?
Uint8 wasKeyPressed(int key) {
    return keyStates[key] == 1;
}

// A tecla foi liberada?
Uint8 wasKeyReleased(int key) {
    return keyStates[key] == 2;
}

void handleInput() {
    resetKeyStates();
    SDL_Event event;
    while (SDL_PollEvent(&event)) {
        switch (event.type) {
            case SDL_QUIT:
                quit = SDL_TRUE;
                break;
            case SDL_KEYDOWN:
                keyStates[event.key.keysym.scancode] = !event.key.repeat;
                break;
            case SDL_KEYUP:
                keyStates[event.key.keysym.scancode] = 2;
                break;
        }
    }
}

void createGame(int w, int h) {
    SDL_Init(SDL_INIT_VIDEO);
    window = SDL_CreateWindow("Window Title", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, w, h, 0);
    renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_PRESENTVSYNC);
}

void destroyGame() {
    SDL_DestroyRenderer(renderer);
    SDL_DestroyWindow(window);
    SDL_Quit();
}

void draw(SDL_Rect* rect, Uint32 color) {
    Uint8 r = (color >> 16) & 0xFF;
    Uint8 g = (color >>  8) & 0xFF;
    Uint8 b = (color)       & 0xFF;
    SDL_SetRenderDrawColor(renderer, r, g, b, SDL_ALPHA_OPAQUE);
    SDL_RenderFillRect(renderer, rect);
}

void collide(SDL_Rect* a, SDL_Rect* b) {
    if ( SDL_HasIntersection(a, b) ) {
        SDL_Rect c;
        SDL_IntersectRect(a, b, &c);
        a->y -= c.h;
    }
}

SDL_Rect player = { 10, 180,  30, 30};
SDL_Rect ground = {  0, 210, 360, 30};

const int VELOCITY   = 5;
const int GRAVITY    = 5;
const int JUMP_FORCE = 80;

void update() {
    player.y += GRAVITY;

    if ( wasKeyPressed(SDL_SCANCODE_SPACE) )
        player.y -= JUMP_FORCE;

    if ( isKeyPressed(SDL_SCANCODE_RIGHT) )
        player.x += VELOCITY;
    else if ( isKeyPressed(SDL_SCANCODE_LEFT) )
        player.x -= VELOCITY;

    collide(&player, &ground);

    draw(&player, 0xFF0000);
    draw(&ground, 0x00FF00);
}

int main(int argc, char *argv[]) {
    createGame(360, 240);

    while ( !quit ) {
        handleInput();
        SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0xFF);
        SDL_RenderClear(renderer);
        update();
        SDL_RenderPresent(renderer);
    }

    destroyGame();
    return 0;
}