Programming Forums > Application Development > C++

DaWei · Nov 6th, 2006, 6:56 PM

Well, it's silly to declare it then define it immediately, since a definition serves. It's when the compiler needs to know how it works BEFORE it's been defined that you use a declaration. You also can't declare one function inside another. move that last brace up.

Incidentally, the names must be in sort for my method to work. If they're not in sort the job is a lot longer.

Why are you asking for comments on something you haven't compiled and tested for yourself?

aznballerlee · Nov 6th, 2006, 7:15 PM

Well, just looking for feedback and going into the right direction in coding. My project is due in a few hours, so I want to finish!

In this case .. I just wanted to make sure if this would work ..

(Toggle Plain Text)

int removeDups(string a[], int n);
int removeDups(string a[], int n)
{

for (i = 0; i < n; ++i)
{
        while ((a[i] == a[i+1])  
        {    
            for (int i = index; i<n; ++i)
           {
               a[i] = a[i+1];
           }
               a[i-1] = "";
         }
}

Jimbo · Nov 6th, 2006, 8:54 PM

Why ask us if it works? You already hinted at having assert statements to test it, so use 'em. As to the code, I prefer the version with 2 functions (mainly for readability reasons)

The Dark · Nov 6th, 2006, 10:00 PM

Depending on your compiler, the fact that you are using "i" everywhere is going to cause you problems.
On a modern compiler, your i's will match up like this:

(Toggle Plain Text)

int removeDups(string a[], int n)
{
  for (i = 0; i < n; ++i)
  {
        while ((a[i] == a[i+1])  
        {    
            for (int i = index; i<n; ++i)
           {
               a[i] = a[i+1];
           }
               a[i-1] = "";
         }
}

See that last red one? At best it will be blanking out the data you want to keep, at worst it will crash your program.

Sane · Nov 6th, 2006, 11:20 PM

The most efficient way is to traverse the array once. Each time you find a duplicate you increment an "offset" variable. Then each iteration you're now shifting the next value by "offset" spaces to the left. That way you only need to traverse the array once, as opposed to yours and DaWei's method which involves traversing the array as many times as there are duplicates. For every duplicate it finds, it's going almost twice as slow as it needs to! Yikes! (DaWei's is not as bad, because it only shuffles as many spaces as it needs to).

Edit: Now that I think of it, this single traversal (although in this situation, nested), may only work on a one dimensional plane where you're checking one item against many. In this situation it is many versus many. I'll think about it a bit more thoroughly when I have the time. Maybe try to code up an example for what I mean.

DaWei · Nov 7th, 2006, 12:29 AM

I definitely want to see this one pass code....

The Dark · Nov 7th, 2006, 12:46 AM

Here you go:

(Toggle Plain Text)

    int to = 0;
    for (i = 1; i < arraySize; ++i)
    {
        if (theNames [i] != theNames [i-1])
          to++;
        if (to != i)
          theNames[to] = theNames[i];
    }
    for (i = to + 1; i < arraySize; ++i)
      theNames[i] = "";

Edit: I guess its 1.n passes really, although you could put the clearing code in the original loop, at the expense of clarity.

Nov 6th, 2006, 6:56 PM	#11
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Well, it's silly to declare it then define it immediately, since a definition serves. It's when the compiler needs to know how it works BEFORE it's been defined that you use a declaration. You also can't declare one function inside another. move that last brace up. Incidentally, the names must be in sort for my method to work. If they're not in sort the job is a lot longer. Why are you asking for comments on something you haven't compiled and tested for yourself? __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Nov 6th, 2006, 7:15 PM	#12
aznballerlee Hobbyist Programmer Join Date: Nov 2006 Posts: 111 Rep Power: 3	Well, just looking for feedback and going into the right direction in coding. My project is due in a few hours, so I want to finish! In this case .. I just wanted to make sure if this would work .. (Toggle Plain Text) int removeDups(string a[], int n); int removeDups(string a[], int n) { for (i = 0; i < n; ++i) { while ((a[i] == a[i+1]) { for (int i = index; i<n; ++i) { a[i] = a[i+1]; } a[i-1] = ""; } } int removeDups(string a[], int n); int removeDups(string a[], int n) { for (i = 0; i < n; ++i) { while ((a[i] == a[i+1]) { for (int i = index; i<n; ++i) { a[i] = a[i+1]; } a[i-1] = ""; } }

Nov 6th, 2006, 8:54 PM	#13
Jimbo Battle Programmer Join Date: Feb 2006 Location: Bellevue, WA, USA Posts: 770 Rep Power: 3	Why ask us if it works? You already hinted at having assert statements to test it, so use 'em. As to the code, I prefer the version with 2 functions (mainly for readability reasons) __________________ <insert disclaimer here> <insert shameless plug for Visual Studio here>

Nov 6th, 2006, 10:00 PM	#14
The Dark Expert Programmer Join Date: Jun 2005 Posts: 894 Rep Power: 4	Depending on your compiler, the fact that you are using "i" everywhere is going to cause you problems. On a modern compiler, your i's will match up like this: (Toggle Plain Text) int removeDups(string a[], int n) { for (i = 0; i < n; ++i) { while ((a[i] == a[i+1]) { for (int i = index; i<n; ++i) { a[i] = a[i+1]; } a[i-1] = ""; } } int removeDups(string a[], int n) { for (i = 0; i < n; ++i) { while ((a[i] == a[i+1]) { for (int i = index; i<n; ++i) { a[i] = a[i+1]; } a[i-1] = ""; } } See that last red one? At best it will be blanking out the data you want to keep, at worst it will crash your program.

Nov 6th, 2006, 11:20 PM	#15
Sane Banned Join Date: Apr 2005 Location: Waterloo, Ontario Posts: 2,101 Rep Power: 6	The most efficient way is to traverse the array once. Each time you find a duplicate you increment an "offset" variable. Then each iteration you're now shifting the next value by "offset" spaces to the left. That way you only need to traverse the array once, as opposed to yours and DaWei's method which involves traversing the array as many times as there are duplicates. For every duplicate it finds, it's going almost twice as slow as it needs to! Yikes! (DaWei's is not as bad, because it only shuffles as many spaces as it needs to). Edit: Now that I think of it, this single traversal (although in this situation, nested), may only work on a one dimensional plane where you're checking one item against many. In this situation it is many versus many. I'll think about it a bit more thoroughly when I have the time. Maybe try to code up an example for what I mean. Last edited by Sane; Nov 6th, 2006 at 11:36 PM.

Nov 7th, 2006, 12:29 AM	#16
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	I definitely want to see this one pass code.... __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Nov 7th, 2006, 12:46 AM	#17
The Dark Expert Programmer Join Date: Jun 2005 Posts: 894 Rep Power: 4	Here you go: (Toggle Plain Text) int to = 0; for (i = 1; i < arraySize; ++i) { if (theNames [i] != theNames [i-1]) to++; if (to != i) theNames[to] = theNames[i]; } for (i = to + 1; i < arraySize; ++i) theNames[i] = ""; int to = 0; for (i = 1; i < arraySize; ++i) { if (theNames [i] != theNames [i-1]) to++; if (to != i) theNames[to] = theNames[i]; } for (i = to + 1; i < arraySize; ++i) theNames[i] = ""; Edit: I guess its 1.n passes really, although you could put the clearing code in the original loop, at the expense of clarity.

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Programming Forums > Application Development > C++

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