Is the Code Simple or Complex In Responsive Web Design?

RWD is not about code its about concept main concept is to make your design portable across many devices as you can Media queries allow the page to use different CSS style rules based on characteristics of the device the site is being displayed on, most commonly the width of the browser.
The fluid grid concept calls for page element sizing to be in relative units like percentages or ems, rather than absolute units like pixels or points.
Flexible images are also sized in relative units (up to 100%), so as to prevent them from displaying outside their containing element.

We can achieve responsive design in different way. You can create it in complex way or simple it is upto your css skills.

1) If you play wisely in css properties and handle with percentages then one same css can be used for all devices. This needs less testing. All devices will handle automatically.

2) Other practice is to handle with different media sizes. Means complex css code development, more testing to check on countless devices.

If you're organized, you'll find things easy at all times. Know the range of devices you're planning to design for, and jot them down. Once you prepare this information you can use it multiple times for different designs. After a few designs you'll have developed a routine and that will make things easier.

This depends on the web project you are working on.

Code in responsive web design is easy to understand and edit.
Tough you need to write a lot of code to make it work across different devices, but still it's very simple.

It all depends on the UI and client's requirements.
The first priority of UX designer is to keep it simple and easy to understand for other coders, if they need to modify it.

Thanks for all of your answers.
is that we can learn how to code responsive and clear our concept , then we can use the Top Framework like Twitter Bootstrap and foundation Framework.
Whats the professional recommendation on it.