Ideas Welcome!

[TitoMB345]

Hey guys, first time poster!

I had a quick question for the masses about a program I am writing: I need to take the input from the user at the keyboard that contains all integers, and then store each integer into an array index.

Example:

User inputs: "10 5 6 7 8 111 2 3"

And I would like to have that turned into an array of

({ 10, 5, 6, 7, 8, 111, 2, 3 })

What is the best way of going about doing this? The number of numbers input by the user is unknown, so I can't do a scanf with a predetermined number of %d's.

Thanks in advance!

[matsp]

So, you don't want a predetermined number of entries - but how will you know how many entries there are? Is it always a single line of numbers? If it's multiple lines, then you DO need some sort of indication that the sequence is finished.

Otherwise, I don't see any problem with it.

--
Mats

[Salem]

Use fgets() to read a whole line.
Use strtol() to convert a single int, and also tell you where to start looking for the next int.

[TitoMB345]

Yes, it is always a single line of numbers input by the user.

I just need the line to be separated into an array of ints with each index at one. I will try what Salem mentioned, thanks!

[matsp]

Yes, it is always a single line of numbers input by the user.

I just need the line to be separated into an array of ints with each index at one. I will try what Salem mentioned, thanks!

That sounds like the sort of solution I would have suggested, but I wanted to clarify the problem first.

--
Mats

[TitoMB345]

Use fgets() to read a whole line.
Use strtol() to convert a single int, and also tell you where to start looking for the next int.

Hmm, okay, so I have strtol() convert the first appearance of an integer into a long... how do I go on from there? How do I tell the program to start looking again passed the integer? The pointer I set in the second argument probably has something to do with it..

[TitoMB345]

Okay, so my latest thought would be somehow using recursion to keep looking for ints until the input is over... hmm.

[matsp]

Okay, so my latest thought would be somehow using recursion to keep looking for ints until the input is over... hmm.

Recursion isn't needed to solve the problem, and as far as I can see, it's not really going to simplify the problem particularly over a while-loop of some sort.

--
Mats

[TitoMB345]

Actually, I ended up using Recursion to fix it!

void sepArrays(char input[], int array[], int *pos) {
   long num = 0;
   char *p;

   num = strtol(input, &p, 10);
   if (num != -2) {
      if (
      array[*pos] = num;
      *pos = *pos + 1;
      sepArrays(p, array, pos);
   }
}

with the initial call to the function being

   sepArrays(input, array, &total);

That solved the problem, and gave me exactly what I needed.


Now the question is though.. is there a more efficient way to do it?

[matsp]

How about this:

int sepArrays(char input[], int array[]) {
   long num = 0;
   char *p = input;
   int pos = 0;

   do {
     num = strtol(p, &p, 10);
     if (num != -2) {
        array[pos] = num;
        pos++;
   } while(num > 0);
   return pos;
}
---
total = sepArrays(input, array);

It should be faster than recursion, it's a line or so shorter in the main code (there's more lines overall, but that's because of the extra variable declaration for pos as a local variable instead of parameter), and I don't see any problem with it.

--
Mats

[anon]

Um, and exactly how does it solve the problem that you don't know how large array needs to be?

And another question: why do you think pos needs to be a pointer?

[matsp]

Anon, that's a good point. I would propose a "guestimate" solution, e.g. select a "should be large enough" array-size, such as 100 or 1000. Just to make it safe, one may want to pass this into sepArray and bail out if the array is filled to the end, rather than overwriting some random other data with more numbers.

There are of course other potential solutions, such as counting the number of integers in the line first. [I have another variation on this that is "really clever", but I'll let that be for a few minutes to see what everyone else can come up with]

[By the way, if we use fgets, how do we know how large to make the input-buffer in the first place? If we assume that this is a hard limit, then the number of integers can not be more than half the length of this string, since each number is at least one digit with one separator character].

--
Mats

[TitoMB345]

Hey guys, thanks again for the help.

You are right, the assignment says to assume there would be no more than 1000 ints entered. So if they enter 1000 ints, the character array would overflow because each character would be 1 space.. I'm not sure how to work around that.

And just to clear the air, there is way more to this assignment than just this part, which I have already flowcharted out, so please don't think I am trying to cheat. I just got stuck at how to come up with the ints into an array.

[matsp]

Hey guys, thanks again for the help.

You are right, the assignment says to assume there would be no more than 1000 ints entered. So if they enter 1000 ints, the character array would overflow because each character would be 1 space.. I'm not sure how to work around that.

So you need to make sure that your input character array is, 4-16000 characters - this depends on what range you reccon the ints to be in - 4 chars for each int covers numers averaging around 50-99, 16 covers "anything". And in a modern machine, a buffer of 16K isn't really that big.

And just to clear the air, there is way more to this assignment than just this part, which I have already flowcharted out, so please don't think I am trying to cheat. I just got stuck at how to come up with the ints into an array.

I think this is fine - we don't do other peoples homework, but giving hints and improving on some existing code is a different thing.

--
Mats