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# Learning C++ by Writing C++

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So I have a class next semester where I need to learn C++. I'll be going through the class textbook too of course, but I hate textbooks because I learn much better by programming than taking notes. I understand there's got to be some reading just to understand the syntax, but I have trouble remembering much from a whole chapter before programming. I prefer to work with smaller bits of information and gradually expand.

So my question is, how could I learn C++ in smaller bits?

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Sounds like you need a good ol' fashioned cup of Don't Worry About It. If you're taking a programming class in school (especially at the university level), you'll have more than enough hands-on programming exercises, assignments/projects, and exams/quizzes to get the practice you need.

If the class is shaping up to be something that doesn't fit your learning style, work with your teacher/professor to get the right instruction for you (which could possibly mean dropping the course, to take it with a different professor.. but I'm getting WAY ahead of myself).

Edited by masskonfuzion

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Due to my experiences over the last four semesters, I think I'm just going to be transferring to another college. That likely won't be until after the next semester though.  I don't have the option to take any of my planned courses with anyone else, and I sign up for 12 credits or higher or my Financial Aid will be cut by more than \$2000.

For instance, we had no chapter quizzes in Computer Architecture this semester despite our professor listing them in the syllabus. we're going to take our final in a few weeks and it will be the first test or quiz we've had in the class. Otherwise he just lectures, or gives fairly random assignments. Once he assumed we (who had no prior ARM programming experience) would be able to write iterative and recursive Fibonacci and Factorial programs in an ARM simulator without a MUL instruction (and many others) in two days. That professor is also my advisor, and he recommended the class to me, and overrode the class requirements despite it requiring content from two other classes I hadn't taken.  Many other classes and professors have had similar sorts of problems.

I don't like to complain about this sort of thing, but I'm really up against a wall here. I had to withdraw from two of four classes this semester to avoid failing grades, and that costs my folks they shouldn't have to spend. My parents also agree with my idea of transferring.

I'm just trying to get a leg up for next semester here, and get ideas for how I can improve.

Edited by RidiculousName

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Hmm, that sounds like an incredibly disorganized teacher/department/curriculum, and/or one that lacks oversight.  If the professor isn't following his own syllabus, that's not a great sign.  Also, it's not customary for professors/advisers to be so liberal with pre-reqs (though it's not unheard of to recommend classes even if you haven't taken the pre-reqs).

Like you, I also had experiences with professors not knowing the prerequisites (mainly adjunct profs who weren't actually employees of the school).  That's a tough situation to be in, but it happens, unfortunately.  It sounds like you do need a more organized program, and one where hopefully the 'bad seed" teachers are held accountable and weeded out.

As for your original question -- how to learn C++ in small bits -- I don't have the definitive answer, but one thing I've done personally is to google for computer science lecture slides/assignments/exams that are available from other schools.  E.g. if you search for "Intro to C++ site:edu", you'll find all kinds of material (the "site:edu" bit limits the search results to those with a domain of .edu).  Your mileage may vary, but hopefully some of the results might fit your learning style.

I wish you the best of luck with your education.

Edited by masskonfuzion

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I see books as sources of information for look-up, rather than a collection of knowledge that I have to learn by heart.

That is, I don't necessarily need to know everything that's in it, but I do need to know what kind of information I can find in it. As a simple example, I would not bother about the precise syntax of a class definition, but I would remember it tells me "basic stuff about classes".

So whenever I have problem falling in the category "basic class problem", I know which book to pick to find the information I need.

It is, as you say, much easier to learn by doing, preferably before you have to make something "for real". I always try to  do a small private project beforehand. Anything that you pick is good, as long as it contains the matter you want to learn about. In a sense, whether the project succeeds isn't even relevant for learning.

As for your education, can't you express your concerns? If you get courses that don't work eg because you didn't have other courses, why not say so? If you got a course chosen, and it doesn't work as proposed, try to find an alternative solution by moving things around and discuss that. If you don't, you're the only person with the problem, so it's in your own interest to speak up.

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I learned C++ by doing the following. This is by no means how you should do it, it's just how my brain is wired.

1. http://www.learncpp.com/
I went to the above site. I read every single article that the person wrote on there, and I wrote my own articles on my personal blog

2. I took a C++ course at my university, and I asked as many questions as possible

3. I bought the book "Jumping into C++"
I believe that the author is the guy that manages www.cprogramming.com, however, I could be mistaken.  The book is cheap (relatively) and not that many pages (my kind of book).

4. I transferred to a position internally at my old company where they needed someone to do some C++ work.
I did this while I started my course at school in C++, and during this time I was reading the book that I mentioned above and I was writing articles on my blog about what I had learned from the site mentioned above, and from other sources.

Overall, regardless of what you know coming into it, with discipline and focus you can pull off anything you want to achieve. By the way, personal projects are your best friend, just try and keep the scope small.

Good luck.

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I followed the same road as Daniel pretty much.

I started with the worse C++ book in the world.  Teach yourself C++ in 24 hours.  24 hours I later signed up for a course at a local community college where I completed two semesters.  I transferred to a job within my company where C/C++ skills were needed.  I continued at the university level.

I have to say the best way to learn this language is by writing code in it.  Find a good book with plenty of exercises and a code examples.  When you start chapter one come up with a generic project of your own...a text based RPG for instance.  Every chapter read, do the exercises and then implement something you learned in the lesson into your project.

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I also learn programming much better by writing programs. "A capar se aprende cortando cojones", my father would say. ("You learn how to castrate by cutting balls.")

I would use the textbook as a list of concepts to learn. Take a look at the table of contents and see what they cover first. Say it's basic integer types and input and output using <iostream> (I have no idea if that's a reasonable place to start, but whoever wrote the book probably has thought about the proper order more than I have). Challenge yourself to do something with that. For instance, try to write  a program that asks the user for 2 integers, adds them up and displays the result. You can learn how to write that however you learn best (tutorials, references, reading sample code...). Once you are satisfied that you understand the concepts, go back to the textbook and read the chapter. Chances are it will be very easy to understand at that point, and there might be things you didn't figure out yourself, or details that you had overlooked.

If you have a hard time getting started, or if you get stuck, or if you want some suggestions for a targeted challenge, you can post here, or you can PM me.

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Basically, the requirements I'm trying to target are:
Composability -- allocators that seamlessly allocate from memory allocated by other allocators.  This helps me to do things like, for example, write an allocator that pads allocations from its parent allocator with bit patterns to detect heap corruption.  It also allows me to easily create spillovers, or optionally assert on overflow with specialized fallbacks.   Handling the fact that some allocators have different interfaces than others in an elegant way.  For example, a regular allocator might have Allocate/Deallocate, but a linear allocator can't do itemized deallocation (but can deallocate everything at once).   I want to be able to tell how much I've allocated, and how much of that is actually being used.  I also want to be able to bucket that on subsystem, but as far as I can tell, that doesn't really impact the design outside of adding a new parameter to allocate calls. Note:  I'm avoiding implementation of allocation buckets and alignment from this, since it's largely orthogonal to what I'm asking and can be done with any of the designs.

To meet those three requirements, I've come up with the following solutions, all of which have significant drawbacks.
Static Policy-Based Allocators
I originally built this off of this talk.
Examples;
struct AllocBlock { std::byte* ptr; size_t size; }; class Mallocator { size_t allocatedMemory; public: Mallocator(); AllocBlock Allocate(size_t size); void Deallocate(AllocBlock blk); }; template <typename BackingAllocator, size_t allocSize> class LinearAllocator : BackingAllocator { AllocBlock baseMemory; char* ptr; char* end; public: LinearAllocator() : baseMemory(BackingAllocator::Allocate(allocSize)) { /* stuff */ } AllocBlock Allocate(size_t size); }; template <typename BackingAllocator, size_t allocSize> class PoolAllocator : BackingAllocator { AllocBlock baseMemory; char* currentHead; public: PoolAllocator() : baseMemory(BackingAllocator::Allocate(allocSize)) { /* stuff */ } void* Allocate(); // note the different signature. void Deallocate(void*); }; // ex: auto allocator = PoolAllocator<Mallocator, size>; Advantages:
SFINAE gives me a pseudo-duck-typing thing.  I don't need any kind of common interfaces, and I'll get a compile-time error if I try to do something like create a LinearAllocator backed by a PoolAllocator. It's composable. Disadvantages:
Composability is type composability, meaning every allocator I create has an independent chain of compositions.  This makes tracking memory usage pretty hard, and presumably can cause me external fragmentation issues.  I might able to get around this with some kind of singleton kung-fu, but I'm unsure as I don't really have any experience with them. Owing to the above, all of my customization points have to be template parameters because the concept relies on empty constructors.  This isn't a huge issue, but it makes defining allocators cumbersome. Dynamic Allocator Dependency
This is probably just the strategy pattern, but then again everything involving polymorphic type composition looks like the strategy pattern to me. 😃
Examples:
struct AllocBlock { std::byte* ptr; size_t size; }; class Allocator { virtual AllocBlock Allocate(size_t) = 0; virtual void Deallocate(AllocBlock) = 0; }; class Mallocator : Allocator { size_t allocatedMemory; public: Mallocator(); AllocBlock Allocate(size_t size); void Deallocate(AllocBlock blk); }; class LinearAllocator { Allocator* backingAllocator; AllocBlock baseMemory; char* ptr; char* end; public: LinearAllocator(Allocator* backingAllocator, size_t allocSize) : backingAllocator(backingAllocator) { baseMemory = backingAllocator->Allocate(allocSize); /* stuff */ } AllocBlock Allocate(size_t size); }; class PoolAllocator { Allocator* backingAllocator; AllocBlock baseMemory; char* currentHead; public: PoolAllocator(Allocator* backingAllocator, size_t allocSize) : backingAllocator(backingAllocator) { baseMemory = backingAllocator->Allocate(allocSize); /* stuff */ } void* Allocate(); // note the different signature. void Deallocate(void*); }; // ex: auto allocator = PoolAllocator(someGlobalMallocator, size); There's an obvious problem with the above:  Namely that PoolAllocator and LinearAllocator don't inherit from the generic Allocator interface.  They can't, because their interfaces provide different semantics.  There's to ways I can solve this:
Inherit from Allocator anyway and assert on unsupported operations (delegates composition failure to runtime errors, which I'd rather avoid).   As above:  Don't inherit and just deal with the fact that some composability is lost (not ideal, because it means you can't do things like back a pool allocator with a linear allocator) As for the overall structure, I think it looks something like this:
Memory usage tracking is easy, since I can use the top-level mallocator(s) to keep track of total memory allocated, and all of the leaf allocators to track of used memory.  How to do that in particular is outside the scope of what I'm asking about, but I've got some ideas. I still have composability Disadvantages:
The interface issues above.  There's no duck-typing-like mechanism to help here, and I'm strongly of the opinion that programmer errors in construction like that should fail at compile-time, not runtime. Composition on Allocated Memory instead of Allocators
This is probably going to be somewhat buggy and poorly thought, since it's just an idea rather than something I've actually tried.
Examples:
struct AllocBlock { void* ptr; size_t size; std::function<void()> dealloc; } class Mallocator { size_t allocatedMemory; public: Mallocator(); AllocBlock Allocate(size_t size) { void* ptr = malloc(size); return {ptr, size, [ptr](){ free(ptr); }}; } }; class LinearAllocator { AllocBlock baseMemory; char* ptr; char* end; public: LinearAllocator(AllocBlock baseMemory) : baseMemory(baseMemory) {end = ptr = baseMemory.ptr;} AllocBlock Allocate(size_t); }; class PoolAllocator { AllocBlock baseMemory; char* head; public: PoolAllocator(AllocBlock baseMemory) : baseMemory(baseMemory) { /* stuff */ } void* Allocate(); }; // ex: auto allocator = PoolAllocator(someGlobalMallocator.Allocate(size)); I don't really like this design at first blush, but I haven't really tried it.

"Composable", since we've delegated most of what composition entails into the memory block rather than the allocator. Tracking memory is a bit more complex, but I *think* it's still doable. Disadvantages:
Makes the interface more complex, since we have to allocate first and then pass that block into our "child" allocator. Can't do specialized deallocation (i.e. stack deallocation) since the memory blocks don't know anything about their parent allocation pool.  I might be able to get around this though.
I've done a lot of research against all of the source-available engines I can find, and it seems like most of them either have very small allocator systems or simply don't try to make them composable at all (CryEngine does this, for example).  That said, it seems like something that should have a lot of good examples, but I can't find a whole lot.  Does anyone have any good feedback/suggestions on this, or is composability in general just a pipe dream?

• Hi
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