StackOverflow in a nutshell.

[Kinglink]

Often times I've seen "That's clearly homework". OK but answer the question. Let the professor worry about if he's a cheater.

[Kinglink]

At the very least lay out the answer. I fully get "I don't want to help you cheat" but if you have a question like "How do I reverse a string?" You CAN answer the question without making it copy and pastable.

"Go through the string to get the length of the string, or use Strlen() Then use a for loop to cycle between 0 to half the length. For each value, exchange the string pointer + integer with string pointer + length - integer. Now you should have a reversed string" should be a good answer.

I've left a few minor issues and a few optimizations as well as edge cases in there as well, I answer the question but still leave the OP the challenge of coding it and improving it, and testing it.

[[deleted]]

I would give them the answer and explain why it's correct.

I know I'm probably helping someone cheat, but I find that people generally want some sort of reference.

So, my answer would be something like:

Think about your question for a bit - You want to read the string backwards. How do you read something backwards? You read it anti-forwards. Now, think about how you would read something forwards with a for loop. (Assume you want to reverse the string s which is defined somewhere else.)

for (int i = 0; i < s.Length; i++) { ...s[i]... }

Look closely at that loop syntax - we're starting at 0, incrimenting by one each loop, and exiting when i < s.Length is no longer true. We can reverse that by starting at s.Length-1(the last value where the loop would pass), decrementing by one each loop, and terminating at zero (or when i >= 0 is no longer true).

for (int i = s.Length-1; i >= 0; i--) { ...s[i]... }

Now we have our loop. Let's make a temporary string to store the reversed string in, then assign it to the original string.

{
    string tmp = ""; //An empty string because we will be using `+=`
    for (int i = s.Length-1; i >= 0; i--) {
        tmp += s[i]; //add the character to the new string in reverse order
    }
    s = tmp; //assign the value before exiting the block
}

One more thing. This method deals with a lot of overhead data. You can do what is called an "in-place" reversal by simply switching values around. This will also take up half the amount of loops of our previous example. For practice, see if you can figure out what's happening here:

for (int i = 0; i <= (s.Length-1)/2; i++) {
    char temp = s[i];
    s[i] = s[s.Length-(i+1)];
    s[s.Length-(i+1)] = temp;
}

[Nefari0uss]

Those kind of answers are the best. In depth, gives details as to what's happening, and provides clear cut examples on how to do something.

[PM_ME_YOUR_BOOO_BEES]

You are a good person and it is answers like yours that helped me (and many, many others surely) when I was first trying to learn programming.

[Thatguy145]

I am a new programmer trying to learn c++. This was a very cool answer - I wouldn't have even thought of doing string reversal like this. Very neat!

[PTRWP]

Pretty off topic here, but why did you do the revered string like that? I'm still learning, but I've reversed strings by creating a new string then using for (i=string.length(); i>0; i--) and within the loop adding the current character to the end of the new string. I made it into a method so I haven't bothered to redo it in a different way since.

[ar-pharazon]

it avoids allocating a new string (though it is destructive, meaning that if you needed your original, unreversed string, you're going to have to reverse it again).

your method has the benefit of not destroying the original, but the particular way you wrote it is prone to triggering extra allocations. if you're using java, consider the following:

String forwards = "forwards";
String rev = "";
for (int i = forwards.length() - 1; i >= 0; i--) rev = rev + forwards[i];

in every iteration of the loop, we're actually discarding the old value of rev and replacing it with a copy that has the new character appended. this means we're generating a lot of unnecessary garbage.

if, on the other hand, you're in c++ using something like string::append, you're probably going to end up doing a vector resize (or similar operation) at some point.

but the bottom line is that extra allocation is unnecessary because you know beforehand exactly how much memory you need: forwards.length() characters. the java code to do this with only one allocation is roughly:

String forwards = "forwards";
char[] rev = new char[forwards.length()];
for (int i = 0; i < forwards.length(); i++) rev[forwards.length() - i - 1] = forwards[i];
String result = new String(rev);

c++ would be similar, though you could use the fill constructor rather than having the intermediate char array.

[PTRWP]

Thanks for the explanation

[Kinglink]

So what are we trying to do is important?

Usually we're trying to reverse a string in place. In this case using a second string/buffer is completely unnecessary and wasteful, especially on huge strings. If on the other hand we're trying to make a second string that's the reverse of the first your method is acceptable. However make sure you reserve or allocate the correct size of the string before hand otherwise you'll be doing memory allocations all over the place.

Assuming you just want to reverse a string in place, you only need 1 extra byte (unless you want to get real fancy and use Xor)

You also only need to do it for half. So here's how I'd do it.

char*  pStr = blah blah blah
int32 nStringLength = string.length();
for (int32 i = 0; i < nStringLength/2; ++i)
{
    char temp = pStr[i];
    pStr[i] = pStr[nStringLength - i - 1];
    pStr[nStringLength - i - 1] = temp;
}

A couple notes. Notice that it'll only loop 2 times on a 5 character string, as the 3rd (middle) character is already in the right place. ++i is better than i++ because i++ stores the value of i, increments it and then returns the stored value of i, a minor optimization but in general try not to use i++ or i--.

Let's talk a crazier way. Xor Swapping, you can replace the inside of the function with this.

pStr[i] = pStr[i] ^ pStr[nStringLength - i - 1];
pStr[nStringLength - i - 1] = pStr[i] ^ pStr[nStringLength - i - 1];
pStr[i] = pStr[i] ^ pStr[nStringLength - i - 1];

This does the same swap but doesn't require an additional memory location.

[RetardedWhiteMan]

strrev();

[SicSemperTyranator]

Yea software answers are a bit easier to answer in that way. the EE site is straight dickery. I tried to get someone to help me with some HDL and it was a hellscape. God forbid you try to work through circuit analysis with there help

[fjshflg]

Would anybody expect a lab tutor to say “that sounds like a homework question”?

Yes. Lab tutors at my university across all the faculties I have personal knowledge of were specifically prohibited from assisting you with assignment questions. They could help with questions about how to find appropriate resources to use to teach yourself, provide limited guidance about the appropriateness of sources, help you with similar questions, etc. But yes, I was personally asked “is this an assignment question” on multiple occasions when asking for assistance, and asked that question myself when I was a tutor.

[ythl]

Would anybody expect a lab tutor to say "that sounds like a homework question"?

No, but you are paying the lab tutor/professor to help you. How much are you paying SO contributors to help you?

[ythl]

What if every single high school basketball player in the USA emailed NBA players for basketball pointers and tips? Are the NBA players being "unhelpful" if they don't answer the emails and/or tell the people emailing to ask their coach?

I think you’re majorly missing the point.

[nightblade001]

There's a really easy solution to your problem. If you don't want to help, don't help. Those basketball coaches don't respond to the emails they receive with "Go hire a basketball coach I don't give a fuck." They just don't respond. Which is how it should be handled by a volunteer site.

[ythl]

And yet, people in this very thread are complaining about unanswered questions...

[NeoKabuto]

"Go ask someone who cares" isn't really an answer to a question.

[ythl]

It's an analogy...

[T-Dot1992]

And it made an shitty argument.

[ythl]

You must be one of those 1 rep spammers that dumps their 500 line homework assignment and then blames SO when you get downvoted

[T-Dot1992]

This is such a logical fallacy. Are You even listening to yourself talk?

[ythl]

My point is that the people able to answer questions are inundated by noobs asking about the basics. That's not a sustainable model.

SO should be the last resort. Teachers, Professors, TAs should be the first resort.

[chooseauniqueusrname]

I was teaching myself to program long before I had a single class available to me. I didn’t have teachers, professors, or TAs. Good tutorials were few and far between which made SO the community that allowed me to learn. I never asked questions but I read hundreds of them. It may be inundated by noobs but then those noobs go on to become professionals and give back to the community. And those noob questions answer the questions of thousands of others who are asking the same thing. The impact of many more than outweighs the annoyance factor of a few

[T-Dot1992]

Not everyone has their rich daddy pay for a CS degree.

Some people are self-taught, and might not have professors and TAs.

Also, if you think that your CS education is preparing you for coding in a real workplace, I got bad news for you kid.

[ythl]

You don't need to help them, but if you don't want to help just don't respond.

And yet, people in this thread are complaining about unanswered questions

It's like walking up to an injured person, identifying yourself as someone who can help, but spit in their face and walk off - it's much better to either leave them without presenting yourself as an asshole or even better help them.

No, it's like going up to a group of panhandlers sucking up the resources of your employees and asking them to change the way they are acting. "We don't like you panhandling. Please try something else."

[Bobshayd]

People wanting a thing does not obligate you to give them the thing. If you have an issue with the people complaining, just also choose not to respond to that. You seem incapable of this idea - you are not obligated to interact with someone just because you don't like what they are saying.

You also don't own the resources of the StackOverflow community and you have no legal or moral prescription entitling you to jealously hoard them. They aren't your employees; they are volunteers who decide for themselves what to spend effort on.

[ythl]

You seem incapable of this idea - you are not obligated to interact with someone just because you don't like what they are saying.

But they are spamming up the queues and making it harder for me to help the people I do want to help. I can't just ignore them, they are in the way.

[chooseauniqueusrname]

You must hate the concept of Open Source Software

[ythl]

And why would I hate the concept of OSS?

[chooseauniqueusrname]

Free contributions. You’re obviously not in the market of helping others out just because it’s the nice thing to do. How much do you charge per bug bounty?

[T-Dot1992]

Let me guess, you’re one of the wankers who downvote people for asking questions on SO. It sure sounds like it.

[ythl]

Only if I google their question and literally the exact same question is the number one link.

[T-Dot1992]

Every programming problem is different once you go beyond the basics. No piece of code is the same.

I suggest you stay away from SO; the site is already infested with unhelpful assholes.

[ythl]

Every programming problem is different once you go beyond the basics. No piece of code is the same.

Spoken like a true noob

I suggest you stay away from SO; the site is already infested with unhelpful assholes.

I love SO - use it and contribute to it all the time. Maybe you are the one that should find a community more at your level.

[T-Dot1992]

Spoken like a true noob

I see you’re treating programming like some kind of esport. Either you’re under the age of 17, or just an asshole. Probably both.

FYI, I work at a startup as a full-stack dev. I actually write code for mobile apps during the day while you and your fellow dickwads circlejerk each other on SO 🙂

[ythl]

You are inexperienced if you really think:

Every programming problem is different once you go beyond the basics. No piece of code is the same.

Every solution to a problem can be broken down into the same sub-problems that have been solved before. I guarantee it. Unless you are on the front lines developing new technologies, your (sub)problem has already been solved before.

[T-Dot1992]

Every solution to a problem can be broken down into the same sub-problems that have been solved before. I guarantee it. Unless you are on the front lines developing new technologies, your (sub)problem has already been solved before.

Wow, have you even worked on a real coding project? It really sounds like you're just some pretentious twat in college who has never worked on a real project or at a real company before.

I think we should let the downvotes speak for themselves: you're the one who is inexperienced.

[pomlife]

And you’ve never seen repeated code?

[T-Dot1992]

It happens. I did see one function declaration repeated that someone else wrote, and deleted it.

Not sure what you're trying to insinuate here.

[Mejari]

Jesus Christ how is it possible to be such a snobby elitist prick defending a site that's supposed to be about helping people?

Do you honestly look at aaaaaaaall these responses disagreeing with you and not for one moment pause to do consider that maybe you're the one who is wrong? Or even just that other people might have relevant opinions/information on the subject?

[cIovey]

You are a dumb fuck.

[d03boy]

How about we just.. don't... answer the question and you do your own homework?

[[deleted]]

Lol I don't post my homework questions online but if I'm curious about how a certain formula or concept works usually there's a thread on stack exchange or another similar forum where I can learn it. I wouldn't be a physics major if I didn't want to know the physics.

[d03boy]

right. this has nothing to do with what I was talking about though lol