coder matlab to C

Hello,

I have problem about coder.

I watched coder video and I just followed example but I can not make C script.

the code is below

function y = ex01(a,b)

y = a*b

that is all...

but when I run coder C....

I received message

Function 'ex01' called with wrong number of arguments: expected 2, received 0.(from matlab 2016)

??? A 'Selected' compiler was not found. You may need to run mex -setup.(from matlab 2013)

please tell me. what is wrong..

Thank you for your reading