Thank you v much vlad,booradley60,jlborges,zero, mikeyboy.
@JLborges: as I m a beginner, I have only one example to refer from the book. I check online but not very clear. (ludicrous: I wish I knew v well & no question posted here...)
@vlad I was confused. I did not know what makes sense and what doesn't.
I change my 3 constructors as advise..
I found the problem that is ...I declare 0 variable, 1 variable, 3 variables constructor but I call the function with 2 variables. so that I got error mismatch function call.
Thank you everybody for giving me advise and I learn more about c++ . All of you are greatly appreciated.