after i sync my iphone to my pc how i find my contacts

If you are syncing your contacts to a supported program they are contained in the program.  If not, they are only contained with your other data and settings in the iPhone backup.  You can't read your contacts from the backup separately; the backup is only there for restoring your phone.  Supported programs include:

Microsoft Outlook 2003, Microsoft Outlook 2007, Microsoft Outlook 2010 (Windows XP, Windows Vista, or Windows 7)Windows Address Book (Windows XP)Windows Contacts (Windows Vista / Windows 7)Address Book (Mac OS X)Microsoft Entourage 2004, Microsoft Entourage 2008, or Microsoft Outlook 2011 for Mac

If you don't have any of these, you can sync your contacts with iCloud or another cloud service (e.g. Google), or you can use an app like My Contacts Backup to back them up.

If you are syncing your contacts to a supported program they are contained in the program.  If not, they are only contained with your other data and settings in the iPhone backup.  You can't read your contacts from the backup separately; the backup is only there for restoring your phone.  Supported programs include:

Microsoft Outlook 2003, Microsoft Outlook 2007, Microsoft Outlook 2010 (Windows XP, Windows Vista, or Windows 7)Windows Address Book (Windows XP)Windows Contacts (Windows Vista / Windows 7)Address Book (Mac OS X)Microsoft Entourage 2004, Microsoft Entourage 2008, or Microsoft Outlook 2011 for Mac

If you don't have any of these, you can sync your contacts with iCloud or another cloud service (e.g. Google), or you can use an app like My Contacts Backup to back them up.