Allegro swap animation with crash guaranteed !

#include <stdio.h>
#include <stdlib.h>
#include <allegro.h>


echanger_gauche_droite(char tab,int i,int j,BITMAP* sprite1,BITMAP* sprite2,BITMAP* buffer){
    double pos_x, pos_y;
    double pos_x_bis, pos_y_bis;
    pos_x = 95+i*36; pos_y = 95+j*36; pos_x_bis = 95+(i+1)*36; pos_y_bis = 95+j*36;
    clear_bitmap(buffer);

    while(pos_x <= pos_x+36){
        while(pos_x_bis >= pos_x-36){
            pos_x += 0.5;
            pos_x_bis -= 0.5;
            clear_bitmap(buffer);
            draw_sprite(buffer,sprite1,pos_x,pos_y);
            draw_sprite(buffer,sprite2,pos_x_bis,pos_y_bis);
            blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H);
        }
    }
}END_OF_FUNCTION();

echanger_haut_bas(char tab,int i,int j,BITMAP* sprite1,BITMAP* sprite2,BITMAP* buffer){
    double pos_x, pos_y;
    double pos_x_bis, pos_y_bis;
    pos_x = 95+i*36; pos_y = 95+j*36; pos_x_bis = 95+i*36; pos_y_bis = 95+(j+1)*36;
    clear_bitmap(buffer);

    while(pos_y <= pos_y+36){
        while(pos_y_bis >= pos_y-36){
            pos_y += 0.5;
            pos_y_bis -= 0.5;
            clear_bitmap(buffer);
            draw_sprite(buffer,sprite1,pos_x,pos_y);
            draw_sprite(buffer,sprite2,pos_x_bis,pos_y_bis);
            blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H);
        }
    }
}END_OF_FUNCTION();



//fonction qui permute deux fruits de droite a gauche
int main()
{
    allegro_init();
    install_keyboard();
    install_mouse();
    set_color_depth(desktop_color_depth());
    set_gfx_mode(GFX_AUTODETECT_WINDOWED,1024,768,0,0);

    int i=0,j=0;
    char tab;
    BITMAP* buffer = NULL;
    BITMAP* apple = NULL;
    BITMAP* onion = NULL;
    BITMAP* orange = NULL;
    BITMAP* fraise = NULL;
    BITMAP* sun = NULL;
    apple = load_bitmap("Apple.bmp",NULL);
    fraise = load_bitmap("Fraise.bmp",NULL);
    onion = load_bitmap("Onion.bmp",NULL);
    sun = load_bitmap("Sun.bmp",NULL);
    orange = load_bitmap("Orange.bmp",NULL);
    buffer = create_bitmap(SCREEN_W,SCREEN_H);

    while(!key[KEY_ESC]){
        clear_bitmap(buffer);
        draw_sprite(buffer,apple,95,95);
        draw_sprite(buffer,fraise,95,95+36);
        blit(buffer,screen,0,0,0,0,SCREEN_W,SCREEN_H);
        while(key[KEY_ENTER]){
        echanger_haut_bas(tab,i,j,apple,fraise,buffer);
        }
    }
}END_OF_MAIN();