#define comparisons and feof.

**Xpl0ReRChR** · 01-12-2012

How do I make this work?

Code:

#define BOUNDARIES 10 20 30 40 50 60 70 80 90 100

index = (newnode->price == BOUNDARIES) ? (newnode->price / 10) - 1 : (int)newnode->price / 10;

Compiler says: expected ')' before numeric constant.

Also, I do this:

Code:

    pos = 1;
    while ((c = fgetc(f)) != EOF) {
        fseek(f, pos - 2, SEEK_CUR);
        fscanf(f, "%s %lf", temp_title, &temp_price);
        insert(titles, prices, temp_title, temp_price);
    }

But the last title and price that are read, are read twice. Why would that be?

It reads from a file where data is in this form:

<TITLE><space><PRICE>
<TITLE><space><PRICE>
<TITLE><space><PRICE>
...

(no spaces in-between title)

**twomers** · 01-12-2012

1) Very simplistically, #define replaces code segments with what its 'label' is defined as. So your

Code:

index = (newnode->price == BOUNDARIES) ? (newnode->price / 10) - 1 : (int)newnode->price / 10;

after preprocessing reads like

Code:

index = (newnode->price == 10 20 30 40 50 60 70 80 90 100) ? (newnode->price / 10) - 1 : (int)newnode->price / 10;

Does that make sense? Nope. So hence an error has occurred.

What you'll have to do is make a function to loop over the list of possible prices, we'll call it findPrice, and compare against the newnode->price value. If it is found return something. Then your index assignment should read something like:

Code:

index = findPrice( newnode->price ) ? newnode->price/10-1 : (int)newnode->price/10;

where you have defined the findPrice function.

2) We'll have to see the insert function before we can judge why it putting it in twice.

**stahta01** · 01-12-2012

When fscanf fails the variables from the last read stay unchanged. So, the last time fails. check the return value to verify it is valid.

Tim S.

**Xpl0ReRChR** · 01-12-2012

@twomers
Yes, but isn't there a more "clever" way of doing that? It would take like 10 switch cases of almost identical code and that would certainly not look good, even though it would work.

"index" must a number from 0 to 9, corresponding to prices (0-10], (10,20] etc (where '(' means not including and '[' means including.)

Which obviously makes my code problematic since 10 would be placed at index = 1, while it needs to be placed at index = 0. That problem would occur for 10, 20, 30, ..., 100, and at 100 in particular it would go out of boundaries.

@stahta
Every title and price are scanned but the last one is scanned twice. As if feof somehow fails to recognise that EOF has been reached. Why is that?

**MK27** · 01-12-2012

It's not clear to me exactly what you want to accomplish, but how about something along these lines?

Code:

int values[] = { 10, 20, 30, 40 }, i;
for (i = 0; i < 4; i++) {
     x == values[i] ? assign; break : continue;
}

This loop is totally wacky looking:

Code:

pos = 1;
while ((c = fgetc(f)) != EOF) {
    fseek(f, pos - 2, SEEK_CUR);
    fscanf(f, "%s %lf", temp_title, &temp_price);
    insert(titles, prices, temp_title, temp_price);
}

What is it you are actually trying to do here? What's the point of "c"? It looks like you are just checking to see if you can read then rewinding. Zany. Not a good method. Forget the fgetc() and just make the condition:

Code:

while (fscanf(f, "%s %lf", temp_title, &temp_price) == 2) {

That may need some tweaking depending on how consistently the file is structured.

**Xpl0ReRChR** · 01-12-2012

@MK27

What the loop is trying to do, is:
- each time, check if end of file has been reached
- if it hasn't been reached, go on and scan the next title and price, then call 'insert' function to insert a new node with these attributes in a linked list.
- if it has been reached, break from loop.

Concerning those values, I roughly explained what I'm trying to do in post #4. Imagine an array where each position will point to the beginning of a linked list. This array has 10 positions: position 1 corresponds to prices (0-10], position 2 corresponds to prices (10-20] and so on.
To find at which position the insertion is to be made, I thought I could do (int)price / 10. So, if the price was 9.21, it would be calculated as 9, divided by 10 and correctly "placed" in the first position. But then I noticed, 10, 20, 30, ..., 100 would be problematic cases since 10/10 would lead to position 1 while I clearly want it to be put in position 0. Same happens with 20/10, 30/10, 40/10, ..., 100/10 (this one in particular would cause a segmentation fault).

So what I'm looking for is a clever way of getting this done without having to create another function to check if the price is one of those mentioned above, or having to use a loop (though I will do what you suggested if I don't find a better way). Is it somewhat more clear to you?

**anduril462** · 01-12-2012

Your read loop ought to just be something like:

Code:

while (fscanf(f, "%s %lf", temp_title, &temp_price) != 2) {
    insert(titles, prices, temp_title, temp_price);
}

It's much simpler and cleaner, and ought to avoid the problem of reading the last one twice.

As for your price category, think about implementing a remainder check as well, perhaps using fmodf.

**nonoob** · 01-12-2012

index = (newnode->price - 1) / 10;

**anduril462** · 01-12-2012

Originally Posted by nonoob

index = (newnode->price - 1) / 10;

That wont quite work. If the item costs $10.50, it should go in index 1, but your code will put it in index 0.

**nonoob** · 01-12-2012

Sorry, the type of newnode->price was not specified. Is it int? double?

**hk_mp5kpdw** · 01-12-2012

Originally Posted by anduril462

Your read loop ought to just be something like:

Code:

while (fscanf(f, "%s %lf", temp_title, &temp_price) != 2) {
    insert(titles, prices, temp_title, temp_price);
}

It's much simpler and cleaner, and ought to avoid the problem of reading the last one twice.

As for your price category, think about implementing a remainder check as well, perhaps using fmodf.

!= ???

**anduril462** · 01-12-2012

Doh! Yeah, that should be == 2. Oops.

**iMalc** · 01-12-2012

Originally Posted by nonoob

Sorry, the type of newnode->price was not specified. Is it int? double?

It would not make sense for it to be a double because there are exact comparisons with mutiples of 10 in there, so I vote for your solution.

**anduril462** · 01-12-2012

Originally Posted by iMalc

It would not make sense for it to be a double because there are exact comparisons with mutiples of 10 in there, so I vote for your solution.

The presence or lack of exact comparisons has little to do with whether it "makes sense" for it to be a double. It's far more likely that the OP simply isn't aware of floating point inaccuracy and the issues of comparing for exact equality. What's actually important in making this decision is the actual data we have to deal with. True, we have no sample data file or declaration of temp_price or the price member of whatever newnode is, but given that the OP:
1. Used %lf to fscanf the data out of the file and
2. Cast the price to an int in the original calculation
it seems reasonable to assume we actually have to deal with prices as doubles.

**Xpl0ReRChR** · 01-12-2012

Thank you guys! Will try that loop out!

And yeah the prices are of type double, that's what's really making this hard. :/

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