How to move a rectangle in SDL2 using C - c

Question

I'm unable to move the rectangle I made in the program. There is no error message in the compiler when I run the program. Can you please tell me what I missed out in the keyboard event. Other event that I assigned to the window works fine. Instead of writing instructions down can you please show me the solution. I have been on this forever. Thanks
#include <SDL.h>
#include <stdlib.h>
int main()
{
SDL_Window *o;
SDL_Renderer *r;
SDL_Event e;
SDL_Rect q;
int i =1;
SDL_Init(SDL_INIT_VIDEO);
o = SDL_CreateWindow("Game test",
SDL_WINDOWPOS_UNDEFINED,
SDL_WINDOWPOS_UNDEFINED,
1024,
800,
SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE);
r = SDL_CreateRenderer(o, -1,SDL_RENDERER_ACCELERATED);
while(i)
{
while(SDL_PollEvent(&e) !=0)
{
if(e.type == SDL_QUIT)
i=0;
else if(e.type == SDL_KEYDOWN)
{
switch(e.key.keysym.sym)
{
case SDLK_ESCAPE:
case SDLK_q:
i=0;
break;
case SDLK_UP:
q.y -=10;
break;
case SDLK_DOWN:
q.y +=10;
break;
case SDLK_RIGHT:
q.x +=10;
break;
case SDLK_LEFT:
q.x -=10;
break;
}
}
}
SDL_SetRenderDrawColor(r,0,0,255,255);
SDL_RenderClear(r);
// Creating the rectangle
q.x=475;
q.y=700;
q.h=50;
q.w=50;
SDL_SetRenderDrawColor(r,0,0,0,255);
SDL_RenderFillRect(r,&q);
SDL_RenderPresent(r);
}
SDL_DestroyWindow(o);
SDL_DestroyRenderer(r);
SDL_Quit();
return 0;
}

Answer 1

You didn't initialize the rectangle object:
SDL_Rect q;
before potentially modifying its values in the event loop, which will result in undefined behavior:
case SDLK_UP:
q.y -=10;
break;
Then any change made to the object is invalidated when you set constant values to it:
q.x=475;
q.y=700;
q.h=50;
q.w=50;
So the solution is clear, set the constant values to the object only when you define it.