How useful is programming in physics? I have been wondering recently how useful programming is to a physicist. It seems fairly useful (simulations are a lot cheaper than the actual thing in many cases) in some areas (say space programs), but in other areas (for example at CERN) it seems pointless. So is it useful and perhaps how do you use it?
 A: An addition to the above answers: I believe there are a couple of ways modern physicists use computers. On the most theoretical level, people use computer algebra systems (CAS) to do lengthy calculations completely or to check results. If you're into theory, you can think of software packages to do tensor manipulations in GR or software that calculates perturbative expansions (trace formulas...) in QFT. Most of the time, these packages don't have an extremely user-friendly interface, so some amount of 'programming' is needed in order to work with them. Furthermore, a lot of theorists use Maple or Mathematica to do/check difficult integrations, solve ODE's, plot graphs quickly...
Then there's the data analysis part: at the end of the day, you're stuck with a heap of data and you'll need to analyze it (manually, in Mathematica, in the language R, ...) and visualize it (in Matlab, using GNUplot, ...).
Next, almost all physicists use simulations once in a while. Theorists like to get a feel for what a non-toy model does, people in hydrodynamics like to see how a flow runs past an obstacle, geophysicists look how the Earth's magnetic field flips chaotically etc. Most of the time, these things can be done using comprehensive software packages (Matlab, Mathematica, ...), but you do need to set up your simulation properly.
Finally, a minority of physicists do simulations for a living. Think of people who calculate collision outcomes at CERN, cosmologists working on numerical relativity, lattice people calculating quark masses etc. This is all typically done in actual programming languages, like C++ or Python, and most of the time on computer clusters.
A: Programming is a skill that some physicists need and others do not. Ditto for knowing your way around a mill or a lathe. Ditto for digital electronics, or contour integrals, or writing popularizations, or vacuum systems.
A: In addition to all has has already been covered, I would like
to tell a word about my own programming experience.
I am an experimental physicist and I've spent a significant fraction of
the past few years programming on the experimental side. A few of the
experiments in our team use non-trivial experimental protocols or
feedback loops, and some have real-time constraints. I spent quite some
time writing and maintaining the software we use for instrument control
and data acquisition, helping others with their scripts (the software is
scriptable and experimental protocols are implemented as scripts) and
interfacing with other instruments that use a variety of protocols and
buses.
A: Programming is immensely useful in any branch of physics.  I don't know where the notion that programming is not useful at CERN comes from (?  Home of the ROOT package, and the internet? Really?  TeraGrid, eh?  1 GB/s of data from the detectors at the LHC won't analyze themselves!), but you may wish to revisit your research on that matter.
I can say that in my 10 years working in physics, there isn't a day that I haven't encountered something related to programming.  From writing scripts to help move along my data processing, to writing applications to interface with a network to collect data, to writing code to analyze data, to, the current bane of my existence, troubleshooting other people's code, I interact with computer programming every day.  And I have never identified with a cartoon more than this one.
So - yes.  I would say that computer programming is immensely useful.  Perhaps my experience is unique, but I doubt it.
A: Programming is extremely important in almost every area of physics. Not every physicist has to be an expert programmer, but many are, and virtually all physicists are at least competent programmers.
In most experiments, the process of data analysis is complex enough to require some programming. More importantly, in many situations, the best (or only) way of telling whether your results are consistent with any given model is to simulate the experiment.
In particular, CERN is absolutely chock-full of programmers analyzing and simulating.
