i forgot my security code for purchasing the apps how can i get it or reset it

Reset what passcode ? What exactly are you being asked for e.g. the card's security code (that code is on the card), Settings > General > Restrictions to re-enable buying (you will have to remember the code, restore to a backup that was taken when the code wasn't on the device, or reset the device back to factory defaults), ... ?

If you mean your security questions, then if you have a rescue email address (which is not the same thing as an alternate email address) set up on your account then the steps half-way down this page give you a reset link on your account : http://support.apple.com/kb/HT5312

If you don't have a rescue email address (you won't be able to add one until you can answer your questions) then you will need to contact iTunes Support / Apple in your country to get the questions reset.

Contacting Apple about account security : http://support.apple.com/kb/HT5699

When they've been reset (and if you don't already have a rescue email address) you can then use the steps half-way down the HT5312 link above to add a rescue email address for potential future use

If you mean the security code on your credit card then you will need to look at your card : http://support.apple.com/kb/HT3541

Thanks..Kind Penguin. I had this problem and didn't realise it was my bank security code they wanted.. if only I could have spoke to a support Operative earlier today ...would have saved me loads of grief... x

Reset my passcode for Apple

How can I reset my passcode to purchase apps on my 5s ipho