allegro programming corner animation

#include<allegro.h>
#include<stdlib.h>
int rect_x=0,rect_y=0;
BITMAP *buffer;
int r=0,b=0,g=0;
int radius=0;
int i=0;
int k=0;
int main()

{
    allegro_init();
    install_keyboard();
    set_color_depth(32);
    if(set_gfx_mode(GFX_AUTODETECT_WINDOWED,1200,700,0,0)!=0)
    {
                                                            set_gfx_mode(GFX_TEXT,0,0,0,0);
                                                            allegro_message("error in initiallization of screen");
                                                            allegro_exit();
                                                            exit(1);
                                                            }
                                                            srand(time(NULL));
                                                            buffer=create_bitmap(SCREEN_W,SCREEN_H);                                                           clear_bitmap(buffer);
                                                            srand(time(NULL));
                                                            rect_x=SCREEN_W/2;
                                                            rect_y=SCREEN_H/2;
                                                           
                                                            while((!key[KEY_ESC]))
                                                            {
                                                                                                 
                                                                                                  r=rand()%200+20;
                                                                                                  g=rand()%255;
                                                                                                  b=rand()%220;
                                                                                                  if(i==350) radius=0,i=0,k=0,clear_bitmap(buffer); 
                                                                                                  arc(buffer,0,SCREEN_H,64,0,radius,makecol(r,g,b));//right to bottom
                                                                                                  arc(buffer,0,0,64,0,radius,makecol(g,b,r));//left to bottom
                                                                                                  arc(buffer,SCREEN_W,0,-64,-128,radius,makecol(b,r,g));//top to left
                                                                                                  arc(buffer,SCREEN_W,SCREEN_H,64,0,radius,makecol(g,g,b));
                                                                                                  //circle(buffer,SCREEN_W/2,SCREEN_H/2,radius,makecol(0,0,0));
                                                                                                  //rect(buffer,rect_x-k,rect_y-k,rect_x+k,rect_y+k,makecol(0,0,0));
                                                                                                  blit(buffer,screen,0,0,0,0,buffer->w,buffer->h);
                                                                                                  radius+=4;
                                                                                                  i++;
                                                                                                  k+=2;
                                                                                                  rest(20);
                                                                                                  }
                                                                                                 
                                                                                                  destroy_bitmap(buffer);
                                                                                               
                                                                                                     }END_OF_MAIN();