Quality Assurance:- Planned and systematic set of 
activities necessary to provide adquate confidence that 
Requirements are properly established.QA is responsability 
of entire team.

Quality Control:- QC is the process in which quality of the 
product/project is compared with applicable standards;and 
action is tacken if any nonconfirm is detected.QC is 
responsability of testing team.

QUALITY ASSURANCE:is a defective preventive method applied 
while the product is under process.generally it is done 
through out the development process.it is used for 
monitoring,measuring and improving the strength of 
development process.

QUALITY CONTROL:is a defect-detection and defect-correction 
method after the product is built.i.e it checks whether the 
product has met all the customer expectations after it is 
built.

Quality Assurance:
1.Concentrates on the process of producing the products.
2.Defect prevention oriented.
3.Usually done throught out the life cycle.
4.This is usually a staff function.
5.Examples-Reviews and Audits.

Quality Control:
1.Concentrates on specific products.
2.Defect-detection and correction oriented.
3.Usually done after the product is built.
4.This is usually a line product.
5.Example-S/W testing at various levels.
Reference:-Page29 in Software Testing & Principles(by
Srinivasan Desikan And Gopalaswamy Ramesh)

QA is process oriented and Qc is product oriented.
QC comes after QA.
QA is defined as a set of activities designed to ensure the
development and maintaince state is adequate and to ensure
that the system will meet its requirements..
QC is defined as a set of activities designed to evaluate
the development of a working product.