SDL collision

[Sharan123]

The code works fine but the thing that i find confusing is the collision function
In line 7: if square's y-axis is greater than the walls y-axis + the wall's height shouldn't there be collision but it returns 0 and still works same is the case for line 9.

 //http://www.youtube.com/user/thecplusplusguy
//Thanks for the typed in code to Tapit85
#include <SDL.h>
 
bool collision(SDL_Rect* square,SDL_Rect* wall)
{
        if(square->y >= wall->y + wall->h)
                return 0;
        if(square->x >= wall->x + wall->w)
                return 0;
        if(square->y + square->h <= wall->y)
                return 0;
        if(square->x + square->w <= wall->x)
                return 0;
        return 1;
}
 
 
 
 
int width = 640;
int height = 480;
 
int main(int argc, char** argv)
{
        SDL_Init(SDL_INIT_EVERYTHING);
        SDL_Surface *screen;
        screen = SDL_SetVideoMode(width, height, 32, SDL_SWSURFACE);
        bool running = true;
        const int FPS = 30;
        Uint32 start;
        bool b[4] = {0,0,0,0};
        SDL_Rect rect;
        rect.x = 10;
        rect.y = 10;
        rect.w = 20;
        rect.h = 20;
        SDL_Rect recarr[5];
        recarr[0].x=70;
        recarr[0].y=0;
        recarr[0].h=200;
        recarr[0].w=10;
 
        recarr[1].x=300;
        recarr[1].y=200;
        recarr[1].h=20;
        recarr[1].w=80;
 
        recarr[2].x=200;
        recarr[2].y=100;
        recarr[2].h=100;
        recarr[2].w=10;
 
        recarr[3].x=40;
        recarr[3].y=300;
        recarr[3].h=20;
        recarr[3].w=60;
 
        recarr[4].x=100;
        recarr[4].y=0;
        recarr[4].h=200;
        recarr[4].w=10;
 
        Uint32 color2 = SDL_MapRGB(screen->format, 0xff,0xff,0xff);
        Uint32 color = SDL_MapRGB(screen->format, 0,0,0);
        for(int i = 0; i < 5; i += 1) {
                        SDL_FillRect(screen,&recarr[i],color2);
        }
        while(running) {
                start = SDL_GetTicks();
                SDL_Event event;
                while(SDL_PollEvent(&event)) {
                        switch(event.type) {
                                case SDL_QUIT:
                                        running = false;
                                        break;
                                case SDL_KEYDOWN:
                                        switch(event.key.keysym.sym) {
                                                case SDLK_UP:
                                                        b[0] = 1;
                                                        break;
                                                case SDLK_LEFT:
                                                        b[1] = 1;
                                                        break;
                                                case SDLK_DOWN:
                                                        b[2] = 1;
                                                        break;
                                                case SDLK_RIGHT:
                                                        b[3] = 1;
                                                        break;
                                       
                                        }
                                        break;
                                case SDL_KEYUP:
                                        switch(event.key.keysym.sym) {
                                                case SDLK_UP:
                                                        b[0] = 0;
                                                        break;
                                                case SDLK_LEFT:
                                                        b[1] = 0;
                                                        break;
                                                case SDLK_DOWN:
                                                        b[2] = 0;
                                                        break;
                                                case SDLK_RIGHT:
                                                        b[3] = 0;
                                                        break;
                                       
                                        }
                                        break;
                        }
                }
 
                SDL_FillRect(screen, &rect, color);
 
                //logic
                if(b[0]) {
                        rect.y--;
                        for(int i = 0; i < 5; i += 1)
                                if(collision(&rect,&recarr[i]))
                                        rect.y++;
                }
                if(b[1]) {
                        rect.x--;
                        for(int i = 0; i < 5; i += 1)
                                if(collision(&rect,&recarr[i]))
                                        rect.x++;
                }
                if(b[2]) {
                        rect.y++;
                        for(int i = 0; i < 5; i += 1)
                                if(collision(&rect,&recarr[i]))
                                        rect.y--;
                }
                if(b[3]) {
                        rect.x++;
                        for(int i = 0; i < 5; i += 1)
                                if(collision(&rect,&recarr[i]))
                                        rect.x--;
                }
 
 
                //render
                SDL_FillRect(screen, &rect, color2);
                SDL_Flip(screen);
 
                if(1000/FPS > SDL_GetTicks()-start) {
                        SDL_Delay(1000/FPS-(SDL_GetTicks()-start));
                }
        }
        SDL_Quit();
        return 0;
}