<apex:page standardController="Account" extensions="AccountExtensionsforcontact" id="pg">

<script type="text/javascript">

function displaymessage()
{
   var a1 = document.getElementById('pg:frm:pb:pbs:a1').value;  //get all the id for pageblock/section/forms etc
alert(''+a1);
if(a1==''){

alert("Remember to Submit changes that you have made!");
}
}

</script>

<apex:form id="frm">
    <apex:pageBlock title="Account Info" id="pb">
        <apex:pageBlockButtons >
            <apex:commandButton value="Save" action="{!save}" onclick="displaymessage(); return false"  />//popup message
            <apex:commandButton value="Go to Contact" action="{!gotocontract}"/>
                </apex:pageBlockButtons>
                <apex:pageBlockSection id="pbs">
        <apex:outputField value="{!Account.name}"/>
        <apex:inputField value="{!Account.phone}" id="a1" />
         <apex:inputField value="{!Account.recordtypeid}" />
        </apex:pageBlockSection>
    </apex:pageBlock>
</apex:form>
</apex:page>

public class AccountExtensionsforcontact {
   public String ids;
   public String id1;
   
    public Account acc {get;set;}
  public Contact  con {get;set;}
     public AccountExtensionsforcontact(ApexPages.StandardController controller) {
  ids=Apexpages.currentPage().getParameters().get('id'); 
   
  acc=[Select id,name,phone from account where id=:ids];
     }
     
     public PageReference gotocontract(){

     PageReference redirect = new PageReference('/apex/Coutacttcreate?id='+ids);
 
    return redirect;
 
     }
         
     

}