SDL collision handling - c++

Question

I have an instance where a SDL_Rect is inside of a big SDL_Rect and i need it to make it so it cannot leave that rect but can still move. The movement of the little rect needs to be like board game movement where you click the button once and it moves a certain cords here is my code:
if( event.type == SDL_KEYDOWN) {
switch( event.key.keysym.sym ) {
case SDLK_UP:
yVel -= 10;
if (!check_collision(box,Cont))
{
std::cout<<"in the water"<<std::endl;
box.y -= yVel - 10;
}
break;
case SDLK_DOWN:
if (!check_collision(box,Cont))
{
std::cout<<"in the water"<<std::endl;
box.y -= yVel + 20;
}
else
{
yVel += 10;
}
break;
case SDLK_LEFT:
xVel -= 10;
if (!check_collision(box,Cont))
{
std::cout<<"in the water"<<std::endl;
}
break;
case SDLK_RIGHT:
xVel += 10;
if (!check_collision(box,Cont))
{
std::cout<<"in the water"<<std::endl;
}
break;
case SDLK_1:
return 2;
break;
}
}

Answer 1

You have inconsistencies in your SDLK_DOWN and the rest of your inputs - no velocity change happens if there are no collisions.
Your input code is changing coordinates, it shouldn't be like that. Make your input code manage the "intent", and have a game loop apply velocity to the object and to the collision detection.
Also, your collision checks should check if I'm at position and I move of delta, will I collide? If I do collide, what's the collision reaction? Do you want the entity to "slide" on collisions or simply stop as soon as a collision is detected?
Considering you are doing a board game, you shouldn't even have to do collision detection. Represent your board as a graph of possible positions your unit can be, translate mouse clicks into board coordinates and calculate the shortest path (use the A* algorithm) between your current position and your destination; invalid clicks (out of bounds) shouldn't translate into movement commands.