[GTAguillaume]

https://sampwiki.blast.hk/wiki/OnDialogResponse
Example:

Code:

public OnDialogResponse(playerid, dialogid, response, listitem, inputtext[])
{
  if(dialogid == 1) //change 1 to your dialog ID
  {
    if(!response) SendClientMessage(playerid, 0xFFFFFFFF, "You canceled!");
    ....
    return 1;
  }
  return 0;
}