In your opinion, what are the most important languages for a programmer to know? I'm talking about concepts, not about how practical the language is.
List the languages and a reason. For example, Lisp for functional programming, JavaScript for prototype-based OOP, etc.
For concepts, I would choose assembler and Java.
The first because you should know in intimate detail how machines work.
The second because you should understand how to shield yourself from the intimate details of the way machines work :-). By that I mean a language with a rich set of data structures at hand (so really Java could be Python, C++ with Boost and so on).
You already mentioned two, here are a few more:
C for understanding how the most other language(-implementations) and operation systems are implemented
Pseudocode for reading/writing documentation. :p
I think knowing C/C++ or any other low level language will help you with understanding the impacts of how managed/script languages works helps. Such as pointers will demystify variable references.
For web programming: PHP, ANSI-SQL, javascript.
Some people may argue that HTML and CSS are not programming languages. But they are esential for web app development.
For Desktop app development, C++ with the Qt Framework. Qt gives C++ the additional "cross-platform" fizz.
Pascal or Basic for start and to master basics of procedural programming.
At school we learned Haskel for functional programming.
And then one should try assembler or C for getting deep and Java for OOP.
A have no arguments for this - that's only my taste and what I tried.
You should start from C and go through C++, Java and the goto WinForms, Then better goto .NET
Well. I'd say learn C and javascript. They are most widely used languages.
You might want to learn Java/some .Net language and/or python/ruby: they're more convenient, tho.
This have the advantage that all those languages are reasonably well designed. For example, don't learn PHP or C++ because they're a mess. They're used widely, you might want to learn them one day, but they can seriously mess with your mind.
I would sat C/C++ cause it sets allot of basics for allot of other languages used around the world.
Personally I learned Java/JavaScript->VB(short course fortunately)->C#->C++, with a pinch of PHP and Perl on top of it all. Best part of that line was C# and then moving behind the scene in C++.
Must know:
1) C (system programming, understanding of machine architecture)
2) Perl or Python or Ruby (practical day-to-day tasks)
3) Java or C# or C++ (OOP, and quite important to get a job these days)
Really important:
1) Haskell or ML (functional programming; changes the way you think)
2) Lisp or Scheme (power of macros)
Nice additionals:
1) Forth (very low-level, explicit stack operation + joy to write your own interpreter)
2) Assembly languages (know how your CPU works)
3) Erlang (parallel processing)
4) Prolog (logic programming)
5) Smalltalk (true OOP and true interactive developent)
I would say:
If you are into distributed systems, I'll consider learning Erlang too. Those are the language I recommend learning, even if only superficial, only for the sake of learning even if you never use them to write a real application.
...And so on.
Its best to know a variety. This gives you a better overall perspective of the art of programming, plus, you get to choose the best tool for the job.
My current list would be:-
It is not the languages rather the paradigms you should know:
If you understood one of these paradigms in one language, it is easy to learn another language in the same paradigm. And there are even more fields specially supported by languages that are important to understand:
At at last you should always know what goes on under the hoods, so you better have a look at assembler.
Look for a set of different programming languages:
It doesn't really matter which ones you choose, but that you choose one from each "category".
You should know a scripting language so that you can prototype your applications faster.
Maybe python/ruby/perl . Groovy is also an alternative if you're a Java guy that likes his java libs.
If you want to understand computers and the underlying hardware, C is the single most important language, commonly said to be the lingua franca of computers. The Stackoverflow podcast tends to cover this at least once a week.
There seem to be enough answers on this, so I'll just leave it at that.
Alot is already mentioned but I would definitely add C++ (already done) for the following reason:
C++ for learning how to use pointers and get the main idea about them.
Although there is the discussion if c++ is still the 'better' language (all depends on what you want to make really) it never hurts to understand pointers, just in case you do need them ever.
Having a scan through the answers so far I'm surprised I've not seen any mention of actionscript.
I think if you learn some C/C++, then some Java then that should prepare you for pretty much all of the decent languages out there. I prefer to see my code in action and I find Actionscript 3 (not 2 or 1) along with Flex (which is MXML) great for quickly demoing visual concepts.
So C & Java helps to learn the syntax of the majority of languages. Actionscript 3 (very similar to java syntax) & MXML for being able to express you code visually very quickly.
Limbo - a programming language with concurrency and channels, what C should have evolved into. ( see also D, another C successor )
No-one else seems to be mentioning any declarative languages, so here are a few:
Prolog - a declarative language for logic programming
Modelica - a declarative OO language for modelling systems.
XSLT - a declarative language for transforming XML.
For parallelism, you don't get much wider than shader language, and the related OpenCL - typically 512 processors in parallel on a high-end desktop, rather than Erlang's 4 processors in parallel ( though with many scheduled processes ).
I think the three languages that best combine practicality and coverage of programming concepts would be
From these languages you can learn low-level system programming, pointers and memory management, static typing, dynamic typing, high-level scripting, event-driven programming, OO programming, functional programming.
Obviously you're not going to get as pure an intro to functional programming as you would with, say, Haskell, but you can learn a lot of the concepts in Python and (especially) Javascript.
A good short list:
Might also include
C - low level system programming plus to understand generic concepts about how memory is handled, stack, stack frame, heap and so on. These are helpful for understanding higher level languages
C++ - mainly std library (separation of generic algorithms and containers), templates, namespaces, but OO concepts as well. Templates meta programming will give you completely different perspective on writing software, this is compile time execution versus run time execution. Templates inheritance (static vs dynamic polymorphism).
Python - dynamic type system, list comprehension - functional programming (?), no memory management for developer, spaces for indentation
Objective-C - message dispatching (can dispatch to nil), dynamic type system (static as well), late binding, OO concepts
It may sound crazy, but I first learned to program writing VBScript macros for windows. I used a template, which is available here http://vbscript-macro-template.blogspot.com/ and I just added to it and also tried to understand everything that it did. Now, several years later I am writing my own desktop and database applications.