write a source code to display the given age is valid, eligible for vote, not eligible for vote or invalid?
if the age is greater than 0 then display valid age, age is less then 17 then display not eligible for vote, if age is greater than 17 then display eligible for vote otherwise invalid age.

What language? What have you tried? Show us some code?

You will want to be using an If statement based on some input. Without seeing what you have done and further information, it's a bit difficult to assist. Aslo, I assume this is a homework question, so you really should show us what effort you have put into this and where you are stuck. While we won't do your homework for you, we are happy to assist and guide when you get stuck or don't understand something.