is there any app like MathCad in apple?

Good place to look for software:

http://www.macupdate.com/

And for free alternatives to some popular software packages:

http://alternativeto.net/

(If you see an ad there for something called MacKeeper, ignore it and on no account install it - it is malware.)

The best there is - but not cheap.

http://www.wolfram.com/mathematica/