Where is qr-code making part?

[wsxdrfv]

So when receive bitcoin, wallet program also shows QR code with address.

How it is possible? How can adopt that system to new coin?

[jnano]

You mean when generating a new address? It's just encoding the address string, possibly with URI features like the scheme prefix (bitcoin:) and a few optional parameters (label, value...)

You can use any QR encoder.

[imjustagirl]

Here is a detailed page about qr codes, where you can read all the information about what they are and how they work.
https://www.qr-code-generator.com
It's just a graphical way to code information in a limited amount of space.
If you are looking to adopt a code into your wallet in order to generate qr codes for your coin adresses, you probably want to look here:
https://github.com/nayuki/QR-Code-generator
This is a QR code generation library and it is available in five different programming languages:  Java, JavaScript, Python, C++, C.
If you are not happy with this one, you can search for more qr code generation libraries.

[demitazh]

you can enter your wallet address here http://zxing.appspot.com/generator/ after that save the image of qrcode generator results, or if you use android, you can download app qrcode generator here https://play.google.com/store/apps/details?id=com.ykart.tool.qrcodegen&hl=en. may be useful

[BardonMe]

Yeah QR codes are pretty easy to make. If you just want one for your address to give people you can use any of the generator links posted already. If you're talking about building a QR code generator into a new altcoin wallet, that's a little more effort.

[Kprawn]

We definitely need some offline QR-code scanner for Bitcoin. {Open Source}

When you frequently use paper wallets, you need to quickly scan a QR-code and sweep them onto a wallet. You do not want

to do this online, because there are inherit risks in doing this. Most "sweeping" of private keys are done with online wallets

and built in QR-code scanners and this is not the ideal method to do this. A lot of the QR-code scanners does not work with

all operating systems.