QA is process oriented and QC is a product oriented.

 Quality Assurance: A set of activities designed to ensure 
that the development and/or maintenance process is adequate 
to ensure a system will meet its objectives. 

  Quality Control: A set of activities designed to evaluate 
a developed working product
 
ex. of qa and qc,i being the testing trainee right now i 
will be under QA activities i.e im in the process of 
getting trained,once i get trained thn i will come under QC 
activities i.e a well trained product is ready and it 
depends of the company 2 accept me or reject me depending 
on the QC.

QA is an 1)external Process
2)It mainly deals in preventing errors.
3)It deals with the quality of the software process itself.
so in a whole u can say QA is set of integrated activites 
which invoves Planning, implementation,assesment, report 
and quality of the product which are defind by the client.

Quality Assurnce is the 'meeting to the standard 
requirement and ensuring that problem has to found and 
fixed".

to meet the customer specification.