Qa is quality assurance. the main responsibility of a QA member is to ensure 
that the standards r followed and to develop the methods as to make the 
software development process smooth and to prevent the bugs from ever 
ocurring.

QC is quality control. the main responsibility of a QC member is to find the 
bugs, find them as early as possible and make sure that they get fixed.

Quality Assurance : A set of activities designed to ensure 
that development and maintaince process is adequate  to 
ensure the system will its requirement. Qa is done by QA 
member. Its to ensure that process is defined and 
appropiate .QA rewie will focus on the process elements  of 
projects. Eg whwther req are defined at proper level or not.


Quality Control :  A set of activities designed to evaluate 
a developed work product. Focus on the Product oriented. 
focus on finding defects in specific deliverables -e.g., 
are the defined requirements the right requirements

Both above two answer are correct but in short we can say
       Quality assurance is a verification phase while 
Quality  control is a validation phase. 




Plz correct me if i m wrong...
Regards..
Lokesh Kumar Chauhan 
lokesh_kumar_chauhan@yahoo.com
Mobile - 09350229669
Noida

Quality Assurance : It is a proces in which every role and
his responsibilities are monitored and guided in such a way
that he accomplishes the task as per guidelines and quality
standards to provide quality of the product at the end.
Quality assurance is also called as Verification.

Quality Control : It is a process in which inspections and
auditings performed on the roles and responsibilities to
segregate bad process and elements from good ones. It is a
one type of controlling process. Quality control is also
called as validation.

Quality Asurance veryfy the all documents

Quality Control to check the application as per requiremant

QA done in  pre_execution period

QC done in post_execution period

QA done by Quality Analiser

QC done by Tester

QA-Quality assurance is a planned and systematic pattern 
for all action necessary to provide adequate confidence 
that the item or product confirms to eshtablish technical 
requirement.

QC-In the quality control we compares the product with 
application standard is to ensure tha all quality 
requirements are being met.

           ---- c.surana82@gmail.com(09986697771)

To say more clearly related to the answer posted by Lokesh
chauhan The verification phase includes information
gathering,Analysis,design and the coding 

the validation phase includes system testing and maintenence.