function timer_Offres(num_offres){
 if(num_offres==nb_offres){
 document.getElementById('offres_photo').innerHTML=tableau_offres[0];
 number_offres=1;
 }
 else{
 document.getElementById('offres_photo').innerHTML=tableau_offres[num_offres];
 number_offres=num_offres + 1;
 }
setTimeout('timer_Offres(number_offres)',3000);
}