Develop Reference

Adding specific numbers from one sequence to another

I feel like this task should not be done this way...
My sequenceY length is not equal to number of steam numbers because you can't assign int[] length with int that have 0 as a starting value.
Therefore my sequenceY have a lot of 0 inside and I can't print the whole sequence. I even tried adding this after for loop:
sequenceY = new int[steamnumbercounter];
But it didn't work ... Why ?
My other question is how do programmers deal with sequences that have unknown length?
I managed to print only steam numbers but the task says print sequenceY not only part of it.
// 4. sequenceX[20] is made of random numbers from 1 to 30 ,
// sequenceY is made of steam numbers from sequenceX. Print sequneceY.
int[] nizx = new int[20];
int[] nizy = new int[20];
int n = 0;
int steamnumbercounter = 0;
Random rnd = new Random();
for (int i = 0; i < nizx.Length; i++)
{
nizx[i] = rnd.Next(1, 30);
if (nizx[i]%2==0)
{
nizy[n] = nizx[i];
n++;
steamnumbercounter++;
}
Console.Write("{0} , ", nizx[i]);
}
for (int i = 0; i < steamnumbercounter; i++)
{
Console.WriteLine("{0} , ",nizy[i]);
}

Partial code review along with an answer.
But it didn't work ... Why ?
That code didn't work because you're reassigning sequenceY to a completely new value.
My other question is how do programmers deal with sequences that have unknown length?
So, with that known we can do a few things here: create an array and use Array.Resize, use a List<T>, fill the initial array then swap it for one of the right size which is filled.
I'm going to assume a "steam" number is an even one.
Your naming is not good: nizx and nizy don't convey the meaning or line up with the problem.
I'm going to demonstrate the last option (since you stated that you don't know how to use many of the moderately complex parts of .NET in this class yet, which is fine): fill the initial array and swap it for a new one. This will run in O(n^2) time (sorta).
So, let's start with our source array.
int[] sequenceX = new int[20];
Next we'll define our destination array to be the same size as our source array. (This is the maximum number of values that could be stored in it, we'll shrink it later.)
int[] sequenceY = new int[sequenceX.Length];
Then we need a variable to hold how many numbers we found that meet our criteria:
int steamNumbers = 0;
And lastly, our Random.
Random random = new Random();
Then, we look through all our sequenceX as you did, but we'll update the logic a bit.
for (int i = 0; i < sequenceX.Length; i++)
{
sequenceX[i] = random.Next(1, 30);
if (sequenceX[i] % 2 == 0)
{
sequenceY[steamNumbers] = sequenceX[i];
steamNumbers++;
}
}
So our code looks almost the same as yours, but we have one more thing to do: since you only want sequenceY to contain steamNumbers we have to shrink it or something.
int[] tempSequenceY = sequenceY;
sequenceY = new int[steamNumbers];
for (int i = 0; i < steamNumbers; i++)
{
sequenceY[i] = tempSequenceY[i];
}
Now sequenceY only has your steam numbers in it.
Final code:
int[] sequenceX = new int[20];
int[] sequenceY = new int[sequenceX.Length];
int steamNumbers = 0;
Random random = new Random();
for (int i = 0; i < sequenceX.Length; i++)
{
sequenceX[i] = random.Next(1, 30);
if (sequenceX[i] % 2 == 0)
{
sequenceY[steamNumbers] = sequenceX[i];
steamNumbers++;
}
}
int[] tempSequenceY = sequenceY;
sequenceY = new int[steamNumbers];
for (int i = 0; i < steamNumbers; i++)
{
sequenceY[i] = tempSequenceY[i];
}
// Print your `sequenceY` here.
You could extract this to a method pretty easily as well:
public int[] GetSteamNumbers(int sequenceCount, int randomMinimum, int randomMaximum)
{
int[] sequenceX = new int[sequenceCount];
int[] sequenceY = new int[sequenceX.Length];
int steamNumbers = 0;
Random random = new Random();
for (int i = 0; i < sequenceX.Length; i++)
{
sequenceX[i] = random.Next(randomMinimum, randomMaximum);
if (sequenceX[i] % 2 == 0)
{
sequenceY[steamNumbers] = sequenceX[i];
steamNumbers++;
}
}
int[] tempSequenceY = sequenceY;
sequenceY = new int[steamNumbers];
for (int i = 0; i < steamNumbers; i++)
{
sequenceY[i] = tempSequenceY[i];
}
return sequenceY;
}
And then call it with:
int[] steamNumbers = GetSteamNumbers(20, 1, 30);
Of course, for the more advanced users (this doesn't help you, but it may help others) we can do something as follows using LINQ:
var random = new Random();
var sequenceY = Enumerable.Range(1, 20)
.Select(x => random.Next(1, 30))
.Where(x => x % 2 == 0)
.ToArray();
Which should have the same effect. (Just demonstrating that there are still things in C# to look forward to in the future.)
Disclaimer: I wrote this entire answer outside of the IDE and without actually compiling it, I make no guarantees to the accuracy of the code but the procedure itself should be fairly straight forward.

The thing with arrays in C# is that they are of fixed size.
You'll have to iterate through and re-create it or use a IEnumerable that has dynamic sizes, such as Lists.
Solution here would be to use a List that contains your integers and then you would use nizx.Add(rnd.Next(1, 30));

Elaborating on my comment above: You can create a 'fake' list by concatenating the values you need in a string, separated by commas. The string.Split(',') will give you the resulting array that you need.
Given a string of form "a,b,c,d" string.Split(',') will create the array ["a","b,"c","d"]. The code:
{
int[] nizx = new int[20];
string numberString = string.Empty;
int n = 0;
Random rnd = new Random();
for (int i = 0; i < nizx.Length; i++)
{
nizx[i] = rnd.Next(1, 30);
if (nizx[i] % 2 == 0)
{
numberString += nizx[i] + ",";
n++;
}
}
var numberArray = numberString.Split(',');
for (int i = 0; i < n; i++)
{
Console.WriteLine("{0} , ", numberArray[i]);
}
}

ArgumentsOutOfRangeExeption in a list<T>

Im getting this exeption thrown when the method is invoked. the list contains exactly 52 objects(number of cards).
Any suggestions what may cause it? maybe the Add and RemoveAt Methods? Or maybe the Random?
The compiler also tell the the problem is in deck.Add(temp[j]); line.
public void Shuffle()
{
List<Card> temp = new List<Card>();
Random rand = new Random();
for (int i = 0; i < 52; i++)
{
for (int j = rand.Next(i, 52); j < 52; j++)
{
temp.Add(deck[j]);
deck.RemoveAt(j);
deck.Add(temp[j]);
}
}
}

Ok, let's imagine we are on the first run through the loops. First iteration of both the outer and inner loop. i is 0, and Rand(i, 52) produces 13.
So we have:
i - 0
j - 13
temp - empty list
deck - assume this is a list with 52 elements
Now let's run the three lines of code inside the loop:
temp.Add(deck[j]);
Get the 13th item of deck and add it to temp. Ok, done. temp now has 1 item.
deck.RemoveAt(j);
Remove the 13th item in deck. Ok, fine.
deck.Add(temp[j]);
Get the 13th item in temp and add it to, wait, what?1? temp only has 1 item! Exception! Exception!.
There isn't a need for the temp list in the first place. There is a very good shuffling algorithm that involves going through the original list of items once (not N times). And you just need one temp variable to hold a value while you swap it with another. Like this:
public void Shuffle()
{
Card temp;
Random rand = new Random();
for (int i = deck.Length; i >= 1; i--)
{
int j = rand.Next(0, i + 1);
temp = deck[i];
deck[i] = deck[j];
deck[j] = temp;
}
}
Done.

If you want to shuffle list of items then you can use the following method:
public static void Shuffle<T>(IList<T> arr, Random rnd)
{
for (var i = 0; i < arr.Count; i++)
{
var j = rnd.Next(i, arr.Count);
var tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
}
This method will help you shuffle your deck without ArgumentsOutOfRangeExeption

temp[j] does not neccessarily exist. You will need to initialize temp so it has at least j+1 entries or you need to change the line of temp[j] to something more fitting.

When you call rand.Next(i, 52), the result could be 52, which would be out of range for your deck and temporary deck.
Also, you need to initialize your temp list, as #nvoigt points out. List has a constructor that takes an integer for the initial size. You could pass in 52. See: http://msdn.microsoft.com/en-us/library/dw8e0z9z(v=vs.110).aspx.
You could have also easily debugged this yourself by looking at the value of j in your debugger.

How do I order the digits 1-10 randomly into an array and then call each part of the array one at a time?

So basically, I need to have the numbers 1-10 randomly ordered upon startup into an array, and on when the form loads, it should load the first number. Each time the user clicks a button, it will load the info associated with the next number.
This is my code, but for some reason it generates a number that is not an integer a lot.
Random rng = new Random(10);
int[] QuestionOrder = new int[10];
for (int i = 0; i < QuestionOrder.Length; i++)
{
int temp = rng.Next(1,10);
while(!(QuestionOrder.Contains(temp)))
{
QuestionOrder[i] = temp;
}
}
each time it generates a number 1 - 10 and checks if it has already been stored in the array, if not, stores it and runs again.
For some reason, its generating numbers that are not integers 1 - 10, and i cant figure out why.

I think you need to overwrite the value of temp inside the while loop and change your range to 1-11 instead of 1-10 and use an if statement before the loop:
int temp = rng.Next(1, 11);
if(!QuestionOrder.Contains(temp)) QuestionOrder[i] = temp;
else
{
while(QuestionOrder.Contains(temp))
{
temp = rng.Next(1, 11);
QuestionOrder[i] = temp;
}
}

You could generate ten random numbers first, then iterate through them.
var rnd = new Random(Environment.TickCount);
var arr = Enumerable.Range(1,10).OrderBy(x => rnd.Next()).ToArray();

this does work nicely
static void Main(string[] args)
{
Random random = new Random();
var range = Enumerable.Range(1, 10).ToList();
int[] rnd = new int[10];
int j = 0;
do
{
int i = random.Next(0, range.Count);
rnd[j++] = range[i];
range.RemoveAt(i);
}
while(range.Count > 1);
rnd[j] = range[0];
}
less cpu intensive than using a contains in a loop

First, your seed is always the same. Either omit it, or use maybe the current date.
Second, you're generating numbers between 1 and 9, so you will never get 10, and one of your array cell will stay empty.
Change temp = rng.Next(1, 11);

As others have pointed out, you're not regenerating a new number when the generated number is already present in the list, leaving you with various default values of 0 in your result.
There are however better ways to 'shuffle' a list of numbers, see Randomize a List in C#:
public static IList<T> Shuffle<T>(this IList<T> list)
{
Random rng = new Random();
int n = list.Count;
while (n > 1)
{
n--;
int k = rng.Next(n + 1);
T value = list[k];
list[k] = list[n];
list[n] = value;
}
return list;
}
Which you can call like this:
IList<int> QuestionOrder = Enumerable.Range(1, 10)
.ToList()
.Shuffle();

The best algorithm to shuffle an array is Knuth-Fisher-Yates, that can be implemented as follows:
public static class Extensions
{
public static void Shuffle<T>(this IList<T> list, Random rand)
{
for (int i = list.Count - 1; i > 0; i--)
{
int n = rand.Next(i + 1);
int tmp = list[i];
list[i] = list[n];
list[n] = tmp;
}
}
}
Usage:
// to get different random sequences every time, just remove the seed (1234)
Random rng = new Random(1234);
// create an array containing 1,2...9,10
int[] questionOrder = Enumerable.Range(1,10).ToArray();
// shuffle the array
questionOrder.Shuffle(rand);
Side note:
To know why Knuth-Fisher-Yates algorithm is better than a naive implementation, read this interesting post by Jeff

Avoiding random duplicates

System.Random generator = new Random(DateTime.Now.Millisecond);
int[] lotteryNumber = new int[7];
Console.WriteLine("Your lottery numbers: ");
for (int i = 0; i<7; i++)
{
lotteryNumber[i] = generator.Next(1, 37);
Console.Write("{0} ",lotteryNumber[i]);
}
Console.ReadLine();
I need to make a program that prints 7 lottery numbers, but without duplicates. The code above prints 7 random numbers in the range of (1-37), but duplicates appaer. I need a way to prevent duplicate numbers from appearing.

The simplest approach IMO would be to generate a sequence of all the possible numbers (i.e. 1-37), shuffle the collection, then take the first seven results.
Searching on Stack Overflow for "Fisher-Yates shuffle C#" will find lots of examples.
In fact, you could modify the Fisher-Yates shuffle to yield results as you took them, so you could write a method such as:
var numbers = Enumerable.Range(1, 37).Shuffle().Take(7).ToList();

You could take a dictionary but make sure that you prevent duplicate key insertion. Keys of dictionary would serve as the unique numbers you need

You could toss them into a HashSet<int>. If you Add and it returns false, generate a new number.

If you're trying to pick numbers from a range without repetitions, you need to create an array of all the possible numbers and then "shuffle" a random selection out:
int[] allPossibleNumbers = Enumerable.Range(1, 37).ToArray();
int[] lotteryNumber = new int[7];
for (int i = 0; i < 7; i++)
{
int index = r.Next(i, 37);
lotteryNumber[i] = allPossibleNumbers[index];
allPossibleNumbers[index] = allPossibleNumbers[i];
// This step not necessary, but allows you to reuse allPossibleNumbers
// rather than generating a fresh one every time.
// allPossibleNumbers[i] = lotteryNumber[i];
}

Generate a list with your 37 items.
Then in your for, select one and delete the selected

Maybe this could help, if you get the existing number just try to find new one that isn't in the array:
static void Main(string[] args)
{
System.Random generator = new Random(DateTime.Now.Millisecond); int[] lotteryNumber = new int[7];
Console.WriteLine("Your lottery numbers: ");
for (int i = 0; i < 7; i++)
{
int lNumber = 0;
do
{
lNumber = generator.Next(1, 37);
}
while (lotteryNumber.Contains(lNumber));
lotteryNumber[i] = lNumber;
Console.Write("{0} ", lotteryNumber[i]);
}
Console.ReadLine();
}

HashSet<int> set = new HashSet<int>();
System.Random generator = new Random(DateTime.Now.Millisecond);
while(set.Count < 7){
set.Add(generator.Next(1,37);
}
That should work, since a HashSet will automatically ignore duplicates. Just loop until the set reaches the number of units you need. Only potential problem is it has the POTENTIAL (unlikely) to loop for a long time, but it should eventually respond.

so I took your original code...found some logic errors and added the fix you were looking for to prevent random number duplicates.
Enjoy!
System.Random generator = new Random(DateTime.Now.Millisecond);
int[] lotteryNumber = new int[7];
int lowerBounds = 1;
int upperBounds = 8;
int maxNumberLotteryValues = 7;
if ( ( upperBounds - lowerBounds ) < (maxNumberLotteryValues))
{
Console.Write("Warning: Adjust your upper and lower bounds...there are not enough values to create a unique set of Lottery numbers! ");
}
else
{
Console.WriteLine("Your lottery numbers: ");
for (int i = 0; i < maxNumberLotteryValues; i++)
{
int nextNumber = generator.Next(lowerBounds, upperBounds);
int count = lowerBounds; //Prevent infinite loop
while ((lotteryNumber.Contains(nextNumber))
&& (count <= upperBounds))
{
nextNumber = generator.Next(lowerBounds, upperBounds);
count++; //Prevent infinite loop
}
lotteryNumber[i] = nextNumber;
Console.Write("{0} ", lotteryNumber[i]);
}
}
Console.ReadLine();

const int nBalls = 37;
const int nPicks = 6;
int[] balls = new int[nPicks];
Random rnd = new Random(DateTime.Now.Millisecond);
int remainingBalls=nBalls;
int remainingPicks=nPicks;
for (int i = 1; i <= nBalls; i++)
{
if (rnd.Next(1, remainingBalls+1) <= remainingPicks)
balls[--remainingPicks]=i;
remainingBalls--;
}
Console.WriteLine(string.Join(",",balls));
Will outperform Shuffle and HashSet methods as nPicks/nBalls gets larger.

Generate some unique numbers and put into array

I'm trying to create a method that produces 10 unique random numbers, but the numbers are not unique, I get several duplicates! How can I improve the code to work as I want?
int[] randomNumbers = new int[10];
Random random = new Random();
int index = 0;
do
{
int randomNum = random.Next(0, 10);
if (index == 0)
{
randomNumbers[0] = randomNum;
index++;
}
else
{
for (int i = 0; i < randomNumbers.Length; i++)
{
if (randomNumbers[i] == randomNum)
break;
else
{
randomNumbers[index] = randomNum;
index++;
break;
}
}
}
}
while (index <= 9);
foreach (int num in randomNumbers)
System.Console.Write(num + " ");
EDIT 2: I have corrected all errors now, but this code isn't working becuase the numbers are not unique! I have updated my code above to the latest version. I preciate some help to solve this! Thanks!

The simplest way to have this is to have an array of the numbers you want (i.e. 1-10) and use a random shuffling algorithm.
The Fisher-Yates shuffle is the easiest way to do this.
EDIT:
Here's a link to a C# implementation: http://www.dotnetperls.com/fisher-yates-shuffle

random.next(0, 10) returns a random number between 0 and 10. It can happen, that it returns the same number multiple times in a row and it is not guaranteed, that you get every number between 0 and 10 exactly one time, when you call it 10 times.
What you want is a list of numbers, every number is unique, between 0 and 9 (or 1 and 10). A possible solution to this would be something like this:
//Create the list of numbers you want
var list = new List<int>();
for(var x = 0; x < 10; x++)
{
list.Add(x);
}
var random = new Random();
//Prepare randomized list
var randomizedList = new List<int>();
while(list.Length > 0)
{
//Pick random index in the range of the ordered list
var index = random.Next(0, list.Length);
//Put the number from the random index in the randomized list
randomizedList.Add(list[index]);
//Remove the number from the original list
list.RemoveAt(index);
}
Explained in words, this is what you do:
Create the list with all the numbers, that your final list should contain
Create a second empty list.
Enter a loop. The loop continues, as long as the ordered list still has numbers in it.
Pick a random index between 0 and list.Length
Put this random number in the randomized list
Remove the item at the index position from the ordered list.
Like this you create the set of numbers you want to have in your randomized list and then always pick a random entry from the ordered list. With this technique, you can also achieve, that certain values occur multiple time in the list.
I'm not sure if my code compiles against c#, as I currently do not have visual studio running here, but I think the code should be mostly correct.

Something like this?
const int maxNumbers = 10;
List<int> numbers = new List<int>(maxNumbers);
for (int i = 0; i < maxNumbers; i++)
{
numbers.Add(i);
}
Random r = new Random();
while (numbers.Count > 0)
{
int index = r.Next(numbers.Count);
Console.Write("{0} ", numbers[index]);
numbers.RemoveAt(index);
}
Console.WriteLine();
Edit: For any random numbers:
const int maxNumbers = 10;
const int biggestNumbers = 10000;
List<int> numbers = new List<int>(maxNumbers);
Random r = new Random();
while (numbers.Count < maxNumbers)
{
int index = r.Next(biggestNumbers);
if (numbers.IndexOf(index) < 0)
{
numbers.Add(index);
Console.Write("{0} ", index);
}
}
Console.WriteLine();