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Why the heck are you allocating an enormous int64 array, when the only place you access it is to get an element out of it - the element value being exactly the same as the index you used to get the element in the first place?
i.e. in all cases newArray[l] == l
It is bad enough that you construct a bool array as well, without allocating a couple of megabytes to hold a number you allready have!
You are aware that a bool is stored as a byte? You might want to consider using a BitArray[^] instead, since that will at least cut your storage by a factor of eight for a very small access overhead.
All those who believe in psycho kinesis, raise my hand.
My ![Badger | [badger,badger,badger,badger...]](https://www.codeproject.com/script/Forums/Images/badger.gif) 's gonna unleash hell on your ass. tastic!
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Well, the number that's being calculated is input by the user and I used a int64 because i wanted the user to be able to use larger numbers.
I know what you mean about the elements though. I never thought of that.
I original thought I needed a 64 array to hold a large digit number in place.
but if an array has no limits i guess the index would be large itself.
So by using a bitarray I can downsize the memory allocated for the user inputed number?
Awesome.
I also figured there was a way to get rid of the bool array by just displaying the current index of the int array when num was true but that would take entire different approach.
This should help me make better code.
thanks for your responses.
Let me redo my code and post back.
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I agree. I find it sometimes disappointing that indices are int32, not int64, especially for BitArray.
BTW: I happen to have been working on an article with over 20 simple ways to calculate prime numbers op to N while focusing on performance. Right now it finds some 5 million primes per second, and that of course is not using a straight sieve (a waste of memory and cycles), but also nothing as advanced as Lucas tests. I should finish the article...
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that. [The QA section does it automatically now, I hope we soon get it on regular forums as well]
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Here is my new and revised Code:
Button Click Event
<br />
private void btnCalculate_Click(object sender, EventArgs e)<br />
{<br />
listPrimes.Items.Clear();<br />
String str = txtN.Text.Trim();<br />
Int64 num;<br />
bool isNum = Int64.TryParse(str, out num);<br />
if (isNum)<br />
{ <br />
Boolean[] boolIndex = new Boolean[num +1];<br />
Int64 newInt = 0;<br />
<br />
foreach (Boolean flag in boolIndex)<br />
{<br />
if (newInt == 0)<br />
{<br />
boolIndex[newInt] = false;<br />
newInt++;<br />
}<br />
else if (newInt == 1)<br />
{<br />
boolIndex[newInt] = false;<br />
newInt++;<br />
}<br />
else<br />
{<br />
boolIndex[newInt] = true;<br />
newInt++;<br />
}<br />
}<br />
<br />
sieveofEratosthenes(boolIndex, num);<br />
}<br />
else<br />
{<br />
MessageBox.Show("Invalid number", "Box for an idiot!");<br />
}<br />
}<br />
The Sieve Prime Detector
<br />
private void sieveofEratosthenes(Boolean[] newBool, Int64 newInt)<br />
{<br />
Int64 numRoot = Convert.ToInt64(Math.Floor(Math.Sqrt(newInt)));<br />
<br />
for (int j = 2; j <= numRoot; j++)<br />
{<br />
<br />
if (newBool[j] == true)<br />
{<br />
Int64 k = j;<br />
<br />
for (Int64 m = 0; m <= newInt; m++)<br />
{<br />
k = k + j;<br />
<br />
if (k <= newInt)<br />
{<br />
newBool[k] = false;<br />
}<br />
}<br />
}<br />
}<br />
for (Int64 l = 0; l <= newInt; l++)<br />
{<br />
if (newBool[l] == true)<br />
{<br />
listPrimes.Items.Add(l);<br />
listPrimes.Refresh();<br />
}<br />
}<br />
<br />
}<br />
Any comments about my code good or bad is greatly appreciated.
modified on Sunday, January 31, 2010 5:39 AM
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A couple of sugestions:
1) You are still using an array of bools => use the BitArray class
2)
Zerodagreez wrote: for (Int64 l = 0; l <= newInt; l++)
{
if (newBool[l] == true)
{
listPrimes.Items.Add(l);
listPrimes.Refresh();
}
}
}
If the number inputed by the user is large the code above will cause a lot of flickering.
use
listPrimes.BeginUpdate()
for (Int64 l = 0; l <= newInt; l++)
{
if (newBool[l] == true)
{
listPrimes.Items.Add(l);
}
}
listPrimes.EndUpdate();
3) Even better than at point 2 you could add it to the list as soon as found.
Put the job/workload in a background worker or separate thread, and from that thread as soon as you find a number that is prime add it to the list
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I tried the bitarray.
It allowed me to set the index to usersNum but would not allow me to set its true or false elements directly as so:
BitArray[] myArray = new bitArray[usersNum];
myArray[0] = false; //error
myArray[1] = false; //error
etc.
Ill check out 3) later. Getting tired.
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Who doesn't 
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Did you actually read up on BitArray at all?
BitArray allNumbers = new BitArray(maxNumber + 1);
for (int i = 0; i < allNumbers.Length; i++)
{
allNumbers.Set(i, true);
}
if (allNumbers[17])
{
MessageBox.Show("Well that one is true!");
}
allNumbers[42] = false;
foreach (bool b in allNumbers)
{
if (!b)
{
MessageBox.Show("But this isn't!");
}
}
All those who believe in psycho kinesis, raise my hand.
My 's gonna unleash hell on your ass. tastic!
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I figured it was just syntax error. 
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An array is indexed by integers regardless of its contained type, so it would be int.MaxValue.
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
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But *right now*, int is the same as Int32, so int.MaxValue will return the same as Int32.MaxValue. When/if they change the default integer size in the compiler to 64-bit, int.MaxValue will be the same as Int64.MaxValue.
I was doing this stuff when int was a 16-bit int, and a long was 32-bit. As a matter of fact, I was doing this stuff when an int was 8-bit, and a long was 16-bit.
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
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The index of any array is Int32, regardless of what type is stored in the array.
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Maybe he'll understand it better if someone else tells him the same thing I did. LOL!
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
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Yea, sorry about that. I did not notice you actually said "the index of" in your statement. My bad. 
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So, if I understand you correctly the max number of indexes allowed in any array is int.maxvalue?
And not how ever many the cpu can hold up to infinity?
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You're trying to use 64 bits to represent one value; I use 64 bits to represent 128 values.
0) Allocate one bit (not an integer, not even a bool) for each number you need to consider.
1) Two is the only even prime number; you only need to consider odd numbers.
In my sieve, I allocate an array of UInt64s and use a formula to determine which bit of which element represents a particular value:
The first bit of a [ 0 ] represents 1
The second bit of a [ 0 ] represents 3
The last bit of a [ 0 ] represents 127
The first bit of a [ 1 ] represents 129
etc.
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I have a treeview and a listbox. For each node, there are some related items in the listbox. I want when the selected node in treeview changes, the items selected in the listbox change too based on the selected treeview node. How can I do that? Briefly, I want that the collection of the selected items in the listbox change in runtime.
I used a code like this:
foreach (DataRowView i in listBox_WorkOverOperationWhichinHole.Items)
{
}
but I do not know what to do next is it a true way to do that!
Thanks a lot in advance!
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You could create a method like PopulateListItems(TreeNode currentNode) and call that method when the treeview selected node changes. The method gets all the child nodes in this example(at least should). You can make it do whatever you want.
something like this for examle:
private void PopulateList(TreeNode tn){
if (tn.Nodes.Count > 0)
{
listView1.BeginUpdate();
listView1.Items.Clear();
foreach(var tr in tn.Nodes)
{
listView1.Items.Add(tr.Text);
}
listView1.EndUpdate();
}
}
And call the method each time the select node changes.
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Mos Dan - Lucian wrote: listView1.Items.Clear();
"I want when the selected node in treeview changes, the items selected in the listbox change too"
there is no listview, it is a ListBox, and it should not be cleared at all.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that. [The QA section does it automatically now, I hope we soon get it on regular forums as well]
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My bad. Not reading cafrefully. But he got the ideea. 
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I would change the listbox to a datagridview. The list box need to be manually loaded rather than data bound.
I would get all the items for display in the DGV into one table and include the key from the tree node. Then you can use a dataview or a bindingsource as the datasource for the DGV and apply a filter to the dataview/bindingsource. The filter would be applied on the treeview selectednodechange event.
Something like this
dataView.RowFilter = string.Format("KeyField = '{0}', TreeNode.Tag);
Never underestimate the power of human stupidity
RAH
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Thank You Both For the Answers!
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How can I have property that have something like this property:
item : (Collection)...
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