During functional Testing if we found any defect we report 
bug to dev team b they will fix and resolve the bug and 
modified build to us

we will executr some of that test cases or total test cases 
which we executed previously

while in funnctional testing we will do many more not only 
regression buyt also retesting n some other

in functional test you(black box tester) check the major
functionalities in his modules are working  are not 

in regression test u check the functionality on the modified
built
if there is problem in the some module u reported the bug to
the developer and after he fixing that issue u do regression
testing on the modified built

executing the same testcases depending on the modification
done  in modules most of the time u go for new test case but
while doing regression testing you check that the
modification done is not effecting any functionlity which
was working fine previously

In Functional Testing, We will execute all the 
functionalities of our application as per our requirements.

Regression Testing - Retesting the application to assure 
that the defects found in Functional testing has not create 
any new bugs and the application is working fine. In most 
of the projects the testers will reexecute all the 
functional test cases.

Dont need to write separate test cases for Functional and 
Regression testing. We can reuse the same test cases for 
both functional and regression.

Functional testing-- In functional testing we will check 
the functionality of the application.

Regression testing--Re execution of the test cases on the 
modified build. that means on modified build we can re test 
the functionality of the application, after defect fixed,is 
there any side effects due to the defect fixing.