Need help with fget

[psychosoren]

I have this problem that I need to get a string from the user and encypt it. The first step is to get the string from the user followed by the enter key. The next step is to encrypt the message at blocks of four characters ( Helllo world! would be [Hell] [o wo] [rld!]. You have to swap character 1 and 4 and 2 and 3. Then this is printed to a file. What I don't understand is how do I just do 4 at a time? I have a very basic program here that gets a sting from a user and prints it to a file. Am I on the right path with this? Should I manipulate the file or is there a step I am missing before the program writes to the file?

 #include <stdio.h>
#define FILENAME "encode.txt"
main()
{
  int c;				
  FILE *encode;					   				
  encode = fopen(FILENAME,"w");
if (encode == NULL){
	printf ("error opening input file\n");
	return 1;}
else
  printf("enter a sequence of characters followed by Return\n");
  while((c=getchar()) != '\n')
   {
      fputc ( c , encode );
    }
  fclose(encode);	
  return 0;		
}

[bithub]

I wouldn't worry about the file at all (for now). Just read in the string from the user, then "encrypt" it, then print the result to the screen.

You will want to read the user string into a buffer (instead of reading in character by character). Use the function fgets() for this.

[Subsonics]

I would start with making a swap function. It seems from your discription that the substrings of 4 chars each will be reversed. What should happen if the string does not even up in multiples of four though?

[psychosoren]

Thank you for the quick responses. If there are three variables then 2 and 3 are swapped. If there are 2 or less they are printed as is.

[jeffcobb]

Even if you have to implement it yourself:

#include <string.h>

char *strrev(char *str)
{
   char *p1, *p2;

   if (! str || ! *str)
      return str;
   for (p1 = str, p2 = str + strlen(str) - 1; p2 > p1; ++p1, --p2)
   {
      *p1 ^= *p2;
      *p2 ^= *p1;
      *p1 ^= *p2;
   }
   return str;
}


int main(int argc, char *argv[])
{
   char *inputString = "Hello World!";
   char workBuf[5];
   int curPos = 0;
   int lastPos = curPos;
   bool bDone = false;
   while(!bDone)
   {
      if( strlen(inputString) <= curPos+4)
      {
	 bDone = true;
      }
      memset(workBuf, 0, 5);
      strncpy(workBuf, inputString+curPos, 4);
      printf("%s", strrev(workBuf));
      curPos += 4;
      if(curPos > strlen(inputString))
      {
	 curPos = strlen(inputString) - lastPos;
      }
      else
      {
	 lastPos = curPos;
      }
   }
	 printf("\nEnd Processing.\n");
   return 0;
}

Note this is a fast hack while I am doing other things so don't blame me if it eats your cat or something ^__^

[bithub]

Even if you have to implement it yourself:

... code ...

Note this is a fast hack while I am doing other things so don't blame me if it eats your cat or something ^__^

Posting a completed homework assignment for somebody doesn't really help anyone. It hurts the ability of the student to think through the assignment on their own, and will only be beneficial to students looking for an easy way out.

It is better to post hints (or pseudo-code) for a general solution, and then give specific help when the student hits a roadblock they cannot overcome on their own.

[jeffcobb]

Posting a completed homework assignment for somebody doesn't really help anyone. It hurts the ability of the student to think through the assignment on their own, and will only be beneficial to students looking for an easy way out.

It is better to post hints (or pseudo-code) for a general solution, and then give specific help when the student hits a roadblock they cannot overcome on their own.

Sorry. I am bad at explaining things/explain them better with code. I learn coding techniques better/faster/more thoroughly when looking at code. I forget that this does not help everyone the same and far be it from me to do someones homework for them.

In this case I would have just thrown strrev() out there until I found that it doesn't exist on UNIX and *that* called for a home-brew version and THAT called for a test harness...

Sigh.

[jeffcobb]

Only other thing I can say in my defense is that when presenting a code solution in a professional situation I develop it using a test-driven development model so the "test" for the solution kinda rides along as proof of execution. Again, I know its not what is needed or apparently desired here and shall endeavor to proof my replies better in the future.

[MK27]

Yo and in Mr.Cobbs defence I do not think providing an example of something should be prohibited or discouraged on a programming advice forum. If universities or whatever want to implement some kind of tracking system to prevent their students from using web resources because they are not getting sufficient education on the premises (and so, perversely, this would amount to cheating the system which is cheating you) then fine.

But I do not think the MAJORITY of us, who ARE NOT IN SCHOOL should be penalized to protect that ridiculousness. There is nothing more annoying than finding someone's blog or tutorial or even API documentation with some long-winded and poorly written explanation of a basic, APPLIED CONCEPT wherein there is NO EXAMPLE CODE!!! For me, and I am sure many others, the surest and quickest way of learning is finding some working code and sorting it out -- indeed, very often I am given to doubt the veracity of someone's "advice" or "demonstration" when they fail to produce at least some basic example WHICH WORKS.

Pathetic...cheers jeffcobb. Altho it would be nice if you put a bit more effort into an accompanying explanation and save the coolio stuff for another time

[quzah]

The problem isn't with providing an example per-say. It's with "HELP!" "Ok, here.".

It's a bad idea to just hand out solutions to every question without requiring effort on the part of the OP to see that they're actually trying to work through the problem. Besides, no one is forcing you to post here.


Quzah.

[MK27]

The problem isn't with providing an example per-say. It's with "HELP!" "Ok, here.".

Yes, god knows we wouldn't want that. I don't see anyone asking someone to do their homework. I see someone with a problem looking for a solution. It is up to them what they do with it and to what extent they try to understand it.

Of course, if you don't like providing that kind of HELP, no one is forcing you to post here either. But I think it is a little sad when you waste your time trying to discourage others from providing legitimate examples of code, because you have some kind of pedantic/ponderous/patronizing/pathetic "teaching" method in mind. You are not really a "wizard". It is not really "magic". Please.

It's a bad idea to just hand out solutions to every question without requiring effort on the part of the OP to see that they're actually trying to work through the problem.

Wow, thank you at least for being honest about your attitude. What were those 4 'p' words?

I think it is better to stick with explaining and demonstrating C in a lucid manner rather than trying to psycho-analyse and second guess the "newbies" Etc

[Elysia]

I'm afraid I have to agree with quzah. Lots of people just copy whatever solution they get without ever understanding it.
Obviously different people learn differently, hence we must first actually discover what type of help they need.
And almost always is it better to post samples that do not actually directly solve the problem and then discuss that. If the OP can assimilate that information, then they are on a good way to solve the actual problem.

But in any case, I would discourage anyone from posting a real solution directly after the question is asked.
After all, we must challenge them a little. That makes a good programmer, to overcome challenges.

[quzah]

I see someone with a problem looking for a solution.

Actually, if you want to be picky, and it appears you do, they asked if they were headed in the right direction. They didn't ask for it to be done for them.

But I think it is a little sad when you waste your time trying to discourage others from providing legitimate examples of code, because you have some kind of pedantic/ponderous/patronizing/pathetic "teaching" method in mind. You are not really a "wizard". It is not really "magic". Please.

Show me again where I'm "discouraging others from providing legitimate examples of code".

What were those 4 'p' words?

And by this point in this discussion, no one knows what the hell you're going on about. If you want to pick a fight with me, and it seems you do from what I've read of your posts regarding me, then have at it already. Otherwise, shut the ........ up.


Quzah.

[MK27]

But in any case, I would discourage anyone from posting a real solution directly after the question is asked.
After all, we must challenge them a little. That makes a good programmer, to overcome challenges.

That's ridiculous. There are plenty of other realms in life in which you can beat around bushes and play games with people. If you want to do that here as well, terrific, but please do not tell people they cannot provide a "straight answer to a straight question" instead.

There is also no end to the "puzzling scenarios" you can encounter while programming, so there is no need to contribute MORE to this. Anyone who is serious about programming will find PLENTY of opportunities to do challenging problem solving on their own, you do not have to provide them with more. A programming forum is somewhere you go when you are at your "wit's end", so to speak. Nice to get past the trivialities quickly and get to the legitimately interesting challanges.

If someone does just want to copy code and not think about it, so what? That's their problem. You do not have to engage in social engineering because you are convinced everyone is just trying to cheat on a homework assignment.

Part of the reason I bring this up is because someone just pulled this one on me on another forum, vis "clearly you are a student who just wants an answer to his question". What BS paranoid crap is that? Yeah, I'm asking for a quick solution to a simple question, hopefully including a quick simple example. That's all. I will understand it. I have plenty of REAL "challanges" to deal with. I do not need basic things obfuscated and mystified by someone who thinks wasting two hours on something that should only take 5 minutes will "teach me something".

Being helpful should mean sharing knowledge, NOT with-holding it.

Actually, if you want to be picky, and it appears you do, they asked if they were headed in the right direction. They didn't ask for it to be done for them..

Point taken, and you're mostly a helpful guy IMO quzah, if snarky, which I don't mind that at all. My earlier comment about being Mr. Mean was a joke

But there should be room for the jeffcobbs of the world as well, without having to belittle and/or censure them.

[Elysia]

It was a shame that you were treated like you were. However, I would think that whoever was replying was at fault rather than the rule for homework. Obviously they mistook you for someone looking for some homework help.
Sharing knowledge is vital and is also why we are here. But there is also sharing too much knowledge if the individual in question has too little understanding. This is a fine line which requires careful guidelines, I think.

I understand your argument, but I would rather guide a newbie to a solution instead of giving them. To experienced programmers, I would give a solution I know of, because I would know they would ask if they didn't understand something of the solution.
And if they simply don't have the required knowledge... well, I can see that you can draw a parallel here to newbies. I consider it safer to give knowledge to experienced programmers, however.
I do know very well how newbies to programming often behave, especially when given solutions. There are a lot of them, and we wouldn't do the world a favor if we let those out into the market.