function check_reg_form_en(){
  var form_ok = true;
  if((document.forms.registration_form.family_name.value=='') && form_ok){
    alert('Please fill in family name.');
    document.forms.registration_form.family_name.focus();
    form_ok = false;
  }
  if((document.forms.registration_form.first_name.value=='') && form_ok){
    alert('Please fill in first name.');
    document.forms.registration_form.first_name.focus();
    form_ok = false;
  }
  
  if((document.forms.registration_form.company.value=='') && form_ok){
    alert('Please fill in company name.');
    document.forms.registration_form.company.focus();
    form_ok = false;
  }
  
  if((document.forms.registration_form.address_street.value=='') && form_ok){
    alert('Please fill in street.');
    document.forms.registration_form.address_street.focus();
    form_ok = false;
  }
  
  if((document.forms.registration_form.address_city.value=='') && form_ok){
    alert('Please fill in city.');
    document.forms.registration_form.address_city.focus();
    form_ok = false;
  }
  if((document.forms.registration_form.address_zip.value=='') && form_ok){
    alert('Please fill in ZIP code.');
    document.forms.registration_form.address_zip.focus();
    form_ok = false;
  }  
  if((document.forms.registration_form.address_country.value=='') && form_ok){
    alert('Please fill in country.');
    document.forms.registration_form.address_country.focus();
    form_ok = false;
  }  
  if((document.forms.registration_form.date_from.value=='' || isNaN(document.forms.registration_form.date_from.value) || document.forms.registration_form.date_from.value < 1 || document.forms.registration_form.date_from.value > 30) && form_ok){
    alert('Please fill in correct arrival date.');
    document.forms.registration_form.date_from.focus();
    form_ok = false;
  }
  if((document.forms.registration_form.date_to.value=='' ||  isNaN(document.forms.registration_form.date_to.value) || document.forms.registration_form.date_to.value < document.forms.registration_form.date_from.value || document.forms.registration_form.date_to.value > 30) && form_ok){
    alert('Please fill in correct departure date (must be bigger than arrival date).');
    document.forms.registration_form.date_to.focus();
    form_ok = false;
  }
  
  if((document.forms.registration_form.no_of_nights.value=='' || isNaN(document.forms.registration_form.no_of_nights.value) || document.forms.registration_form.no_of_nights.value < 0 /*|| document.forms.registration_form.no_of_nights.value > document.forms.registration_form.date_to.value - document.forms.registration_form.date_from.value*/) && form_ok){
    alert('Number of nights seems not to be correct.');
    document.forms.registration_form.no_of_nights.focus();
    form_ok = false;
  } 
  if((document.forms.registration_form.no_of_acc_persons.value=='' || isNaN(document.forms.registration_form.no_of_acc_persons.value) || document.forms.registration_form.no_of_acc_persons.value < 0 ) && form_ok){
    alert('Number of accompanying persons seems not to be correct.');
    document.forms.registration_form.no_of_acc_persons.focus();
    form_ok = false;
  } 

  return form_ok;

}



function check_reg_form_en2(){
  var form_ok = recalculate();
  
  if((document.forms.registration_form.personal_family_name.value=='') && form_ok){
    alert('Please fill in family name.');
    document.forms.registration_form.personal_family_name.focus();
    form_ok = false;
  }
  if((document.forms.registration_form.personal_first_name.value=='') && form_ok){
    alert('Please fill in first name.');
    document.forms.registration_form.personal_first_name.focus();
    form_ok = false;
  }
  
  if((document.forms.registration_form.personal_company_name.value=='') && form_ok){
    alert('Please fill in company name.');
    document.forms.registration_form.personal_company_name.focus();
    form_ok = false;
  }
 
  if((document.forms.registration_form.personal_company_address_street.value=='') && form_ok){
    alert('Please fill in street.');
    document.forms.registration_form.personal_company_address_street.focus();
    form_ok = false;
  }
  
  if((document.forms.registration_form.personal_company_address_city.value=='') && form_ok){
    alert('Please fill in city.');
    document.forms.registration_form.personal_company_address_city.focus();
    form_ok = false;
  }
  if((document.forms.registration_form.personal_company_address_zip.value=='') && form_ok){
    alert('Please fill in ZIP code.');
    document.forms.registration_form.personal_company_address_zip.focus();
    form_ok = false;
  }  
  if((document.forms.registration_form.personal_company_address_country.value=='') && form_ok){
    alert('Please fill in country.');
    document.forms.registration_form.personal_company_address_country.focus();
    form_ok = false;
  }  
  if((document.forms.registration_form.personal_company_address_phone.value=='') && form_ok){
    alert('Please fill in phone No.');
    document.forms.registration_form.personal_company_address_phone.focus();
    form_ok = false;
  }  
  if((document.forms.registration_form.personal_company_address_email.value=='') && form_ok){
    alert('Please fill in email address.');
    document.forms.registration_form.personal_company_address_email.focus();
    form_ok = false;
  }  
  
  if((isNaN(document.forms.registration_form.registration_fee_total.value) || document.forms.registration_form.registration_fee_total.value < 1) && form_ok){
    alert('Please select your registration type.');
    document.forms.registration_form.registration_fee_author.focus();
    form_ok = false;
  }  
  
  if (form_ok){
    document.forms.registration_form.registration_fee_total.disabled = false; 
    document.forms.registration_form.presentation_fee_total.disabled = false; 
    document.forms.registration_form.sum_registration.disabled = false;   
    document.forms.registration_form.sum_presentation.disabled = false;  
    document.forms.registration_form.sum_accommodation.disabled = false; 
    document.forms.registration_form.sum_total.disabled = false; 
  }
  return form_ok;
}

function setEmpty(){
  document.forms.registration_form.registration_fee_total.value = ''; 
  document.forms.registration_form.presentation_fee_total.value = ''; 
  document.forms.registration_form.sum_registration.value = '';  
  document.forms.registration_form.sum_presentation.value = ''; 
  document.forms.registration_form.sum_accommodation.value = ''; 
  document.forms.registration_form.sum_total.value = ''; 
}

function recalculate(){  
  if (document.forms.registration_form.registration_fee_author.value == ''){
    author_fees = 0;
  }  
  else{  
    if (isNaN(document.forms.registration_form.registration_fee_author.value) || document.forms.registration_form.registration_fee_author.value < 1){
      alert('Please type a numeric value into field Registration fee-author');
      document.forms.registration_form.registration_fee_author.focus();
      setEmpty();
      return false;
    }
    else{
      author_fees = parseInt(document.forms.registration_form.registration_fee_author.value);
    }
  }   
  
  if (document.forms.registration_form.registration_fee_participant.value == ''){
    participant_fees = 0;
  }  
  else{  
    if (isNaN(document.forms.registration_form.registration_fee_participant.value) || document.forms.registration_form.registration_fee_participant.value < 1){
      alert('Please type a numeric value into field Registration fee-participant');
      document.forms.registration_form.registration_fee_participant.focus();
      setEmpty();
      return false;
    }
    else{
      participant_fees = parseInt(document.forms.registration_form.registration_fee_participant.value);
    }
  }  
  
  if (document.forms.registration_form.registration_fee_student.value == ''){
    student_fees = 0;
  }  
  else{  
    if (isNaN(document.forms.registration_form.registration_fee_student.value) || document.forms.registration_form.registration_fee_student.value < 1){
      alert('Please type a numeric value into field Registration fee-student');
      document.forms.registration_form.registration_fee_student.focus();
      setEmpty();
      return false;
    }
    else{
      student_fees = parseInt(document.forms.registration_form.registration_fee_student.value);
    }
  }   
  
  if (document.forms.registration_form.registration_fee_acompanying.value == ''){
    acompanying_fees = 0;
  }  
  else{  
    if (isNaN(document.forms.registration_form.registration_fee_acompanying.value) || document.forms.registration_form.registration_fee_acompanying.value < 1){
      alert('Please type a numeric value into field Registration fee-acompanying person');
      document.forms.registration_form.registration_fee_acompanying.focus();
      setEmpty();
      return false;
    }
    else{
      acompanying_fees = parseInt(document.forms.registration_form.registration_fee_acompanying.value);
    }
  }         
   
  total_registration_fees = author_fees + participant_fees + student_fees + acompanying_fees;
  
  if (document.forms.registration_form.presentation_fee_poster.value == ''){
    poster_fees = 0;
  }  
  else{  
    if (isNaN(document.forms.registration_form.presentation_fee_poster.value) || document.forms.registration_form.presentation_fee_poster.value < 1){
      alert('Please type a numeric value into field Registration fee-acompanying person');
      document.forms.registration_form.presentation_fee_poster.focus();
      setEmpty();
      return false;
    }
    else{
      poster_fees = parseInt(document.forms.registration_form.presentation_fee_poster.value);
    }
  }    
  
  if (document.forms.registration_form.presentation_fee_proceedings.value == ''){
    proceedings_fees = 0;
  }  
  else{  
    if (isNaN(document.forms.registration_form.presentation_fee_proceedings.value) || document.forms.registration_form.presentation_fee_proceedings.value < 1){
      alert('Please type a numeric value into field Registration fee-acompanying person');
      document.forms.registration_form.presentation_fee_proceedings.focus();
      setEmpty();
      return false;
    }
    else{
      proceedings_fees = parseInt(document.forms.registration_form.presentation_fee_proceedings.value);
    }
  } 
  total_presentation_fees = poster_fees + proceedings_fees;      
  
  if (document.forms.registration_form.accommodation_fee_total.value == ''){
    total_accommodation_fees = 0;
  }  
  else{  
    if (isNaN(document.forms.registration_form.accommodation_fee_total.value) || document.forms.registration_form.accommodation_fee_total.value < 1){
      alert('Please type a numeric value into field Registration fee-acompanying person');
      document.forms.registration_form.accommodation_fee_total.focus();
      setEmpty();
      return false;
    }
    else{
      total_accommodation_fees = parseInt(document.forms.registration_form.accommodation_fee_total.value);
    }
  } 
  
  total = total_registration_fees + total_presentation_fees + total_accommodation_fees;
  document.forms.registration_form.registration_fee_total.value = total_registration_fees; 
  document.forms.registration_form.presentation_fee_total.value = total_presentation_fees; 
  document.forms.registration_form.sum_registration.value = total_registration_fees;  
  document.forms.registration_form.sum_presentation.value = total_presentation_fees; 
  document.forms.registration_form.sum_accommodation.value = total_accommodation_fees; 
  document.forms.registration_form.sum_total.value = total; 
  return true;
}