On my app a teacher can have several classes, and when I exclude a teacher's profile I have to, first, delete his classes. I'm trying to put each class_id of this teacher on an int array, to later delete all classes which the id is contained inside this array.
This is my code so far:
int x = 0;
int[] count = new int[x];
while (reader_SelectedClasses.Read())
{
if(x != 0)
{
x++;
count = new int[x];
}
count[x] = _class.Class_id = reader_SelectedClasses.GetInt16("class_id");
}
And this is what
reader_SelectedClasses.Read()
does:
select class_id from tbl_class where user_id = " + id + ";
And this is the return, when I try this on MySQL:
But it gives me back an IndexOutOfRangeException when I run the code on my DAO class. What am I missing? Already went here but didn't quite understand. Can someone please explain on few words and post and fixed code for this?
You need to learn how to use a debugger and step through your program.
count = new int[x]; discards what was in count and creates a new array that contains zeroes. This array's indexes go from 0 to x - 1.
count[x] = ... sets the array element at index x which according to the previous line is one past the end of the array.
You need to set count = new int[x] only once, at the beginning of your program, and set count[x] = ... only if x >= 0 and x < count.Length.
You are getting IndexOutOfRange Exception because you are trying to access element from array which is out of range.
At first line you are setting x = 1. Hoping that controller enters while loop and as x is 1 it doesn't enter if loop and it executes next statement. But count[1] (x = 1) is not allowed as you have created array with only one element and that you can access with count[0]. (Array indexing starts from 0)
You are trying to achieve a List behavior with an array.
Obviously, the IndexOutOfRangeException is because you initialize an empty array and then try to add values to it in a non-existing cell.
Try to convert to List<int>:
List<int> count = new List<int>();
while (reader_SelectedClasses.Read())
{
int classId = _class.Class_id = reader_SelectedClasses.GetInt16("class_id");
count.Add(classId);
}
If you really need an array out of it you can do:
int[] countArray = count.ToArray()
Related
everyone. I've this small task to do:
There are two sequences of numbers:
A[0], A[1], ... , A[n].
B[0], B[1], ... , B[m].
Do the following operations with the sequence A:
Remove the items whose indices are divisible by B[0].
In the items remained, remove those whose indices are divisible by B[1].
Repeat this process up to B[m].
Output the items finally remained.
Input is like this: (where -1 is delimiter for two sequences A and B)
1 2 4 3 6 5 -1 2 -1
Here goes my code (explanation done via comments):
List<int> result = new List<int>(); // list for sequence A
List<int> values = new List<int>(); // list for holding value to remove
var input = Console.ReadLine().Split().Select(int.Parse).ToArray();
var len = Array.IndexOf(input, -1); // getting index of the first -1 (delimiter)
result = input.ToList(); // converting input array to List
result.RemoveRange(len, input.Length - len); // and deleting everything beyond first delimiter (including it)
for (var i = len + 1; i < input.Length - 1; i++) // for the number of elements in the sequence B
{
for (var j = 0; j < result.Count; j++) // going through all elmnts in sequence A
{
if (j % input[i] == 0) // if index is divisible by B[i]
{
values.Add(result[j]); // adding associated value to List<int> values
}
}
foreach (var value in values) // after all elements in sequence A have been looked upon, now deleting those who apply to criteria
{
result.Remove(value);
}
}
But the problem is that I'm only passing 5/11 tests cases. The 25% is 'Wrong result' and the rest 25% - 'Timed out'. I understand that my code is probably very badly written, but I really can't get to understand how to improve it.
So, if someone more experienced could explain (clarify) next points to me it would be very cool:
1. Am I doing parsing from the console input right? I feel like it could be done in a more elegant/efficient way.
2. Is my logic of getting value which apply to criteria and then storing them for later deleting is efficient in terms of performance? Or is there any other way to do it?
3. Why is this code not passing all test-cases or how would you change it in order to pass all of them?
I'm writing the answer once again, since I have misunderstood the problem completely. So undoubtly the problem in your code is a removal of elements. Let's try to avoid that. Let's try to make a new array C, where you can store all the correct numbers that should be left in the A array after each removal. So if index id is not divisible by B[i], you should add A[id] to the array C. Then, after checking all the indices with the B[i] value, you should replace the array A with the array C and do the same for B[i + 1]. Repeat until you reach the end of the array B.
The algorithm:
1. For each value in B:
2. For each id from 1 to length(A):
3. If id % value != 0, add A[id] to C
4. A = C
5. Return A.
EDIT: Be sure to make a new array C for each iteration of the 1. loop (or clear C after replacing A with it)
I'm working on a football league fixture project on C# Console Application.
I'm trying to choose random teams from the array which contains the teams which plays at their home and away.
When I'm trying to generate 9 random numbers, only 8 numbers are generated and 0 are not, so the code can't break the for loop.
I suppose that the problem is that the if statement does not allow to generate the same number and int array's elements' default value is 0.
Here is the code and the output:
C# Code Output
int randomHome; //Random number genetator for choosing a random iteration value from home array which containss the teams which plays at their home
int randomAway; //Random number genetator for choosing a random iteration value from awayarray which containss the teams which plays at away
Random randomNum = new Random();
int[] randomHomeNumArray = new int[home.Length]; //array will hold the randomHome values and home array is the array which is holding the team's iteration values which plays at their home
int[] randomAwayNumArray = new int[away.Length]; //array will hold the randomAway values and away array is the array which is holding the team's iteration values which plays at away
for (int homeArrayCounter = 0; homeArrayCounter < randomHomeNumArray.Length; homeArrayCounter++)
{
randomHome = randomNum.Next(home.Length)
if (!randomHomeNumArray.Contains(randomHome) )
{
randomHomeNumArray[homeArrayCounter] = randomHome; //It will hold the randomHome values
Console.WriteLine(homeArrayCounter + ". iterasyon in Home " + randomHomeNumArray[homeArrayCounter]);
}
else
{
homeArrayCounter--;
}
}
Console.WriteLine("\n\n");
for (int awayArrayCounter = 0; awayArrayCounter < randomAwayNumArray.Length; awayArrayCounter++)
{
randomAway = randomNum.Next(randomAwayNumArray.Length);
if (!randomAwayNumArray.Contains(randomAway))
{
randomAwayNumArray[awayArrayCounter] = randomAway; //It holds the random valures from away array which contains the teams which plays at away
Console.WriteLine(awayArrayCounter + ". iterasyon in Away " + randomAwayNumArray[awayArrayCounter]);
}
else
{
awayArrayCounter--;
}
}
When you initalize an array, it has the value 0 by default for each index. When you are using the random number, it always skips 0 because it already exists.
You can try like this:-
for(int i= 0; i<randomHomeNumArray.Length; i++){
randomHomeNumArray[i] = -1;
}
for (int homeArrayCounter = 0; homeArrayCounter < randomHomeNumArray.Length; homeArrayCounter++)
{
do{
randomHome = randomNum.Next(home.Length);
} while(!randomHomeNumArray.Contains(randomHome));
randomHomeNumArray[homeArrayCounter] = randomHome; //It will hold the randomHome values
Console.WriteLine(homeArrayCounter + ". iterasyon in Home " + randomHomeNumArray[homeArrayCounter]);
}
It appears you're trying to just randomize arrays.
Try this instead:
Random randomNum = new Random();
int[] randomHomeNumArray = Enumerable.Range(0, home.Length).OrderBy(_ => randomNum.Next()).ToArray();
int[] randomAwayNumArray = Enumerable.Range(0, away.Length).OrderBy(_ => randomNum.Next()).ToArray();
That's it. Done.
Your problem is the default initialization of your arrays:
int[] randomHomeNumArray = new int[home.Length];
This creates an array filled with 0s, because 0 is the default value for int.
So your if condition
if (!randomHomeNumArray.Contains(randomHome))
is always false for 0 because 0 is already contained in the array.
You may initialize your arrays instead like this:
int[] randomHomeNumArray = Enumerable.Repeat(-1, home.Length).ToArray();
So you fill it with -1 instead of 0 and your if condition works.
Because int is not a null-able data type, by default, an int[] gets initialized with zeroes. So even if you think it's an empty array, it's actually an array with all elements set to zero.
To rectify the problem, you can consider using an int?[] (null-able int array) instead. Or, you can initialize the array with either a negative integer or some integer greater than the maximum inclusive upper bound. Better yet, to achieve what you want, in a better way, use the solution provided by #Enigmativity, and mark his answer accepted, if it helped.
I'm running this code, but every time, I get the error "An unhandled exception of type 'System.ArgumentOutOfRangeException' occurred" on the first line of the for loop. Its basically code for a multiple choice quiz question, with questions & answers stored in a 2d array.
Unfortunately, I can't seem to spot the problem. It's probably a simple error, but I'm a beginner so I'm struggling to spot it.
I've read through similar questions, but I don't understand why this line is causing problems. I've got 4 elements in my list, one is removed before the loop, so there should be 3 left. I'm only looping through 3 times, so I don't understand what the problem is.
Hopefully someone will be able to help, Thanks!
Random rndq = new Random();
Random rnda = new Random();
List<int> answers = new List<int> { 1, 2, 3, 4 };
int questionchoice = rndq.Next(0, questions.GetLength(0) - 1);
int labelchoice = rnda.Next(0, answers.Count-1);
lblQuestion.Text = questions[questionchoice, 0];
var answer = (Label)Controls["lblAns" + answers[labelchoice]];
answer.Text = questions[questionchoice, 1];
answers.Remove(labelchoice);
int j = 2;
for (int i = 0; i < 3; i++)
{
var wronganswers = (Label)Controls["lblAns" + answers[i]];
wronganswers.Text = questions[questionchoice, j];
answers.RemoveAt(i);
j++;
}
Each pass through the loop you're removing an item from the list. After the first pass your list has 3 items in it [2, 3, 4]. Next pass there are two items left [2, 4]. Then you try to get the third item from the list of two and get an exception.
Either you need to leave the list alone while looping or make sure that your loop condition actually references the length of the list. Assuming that you want to actually process all 4 items I would suggest that you remove the RemoveAt call completely.
Or if you actually want to remove the items, reverse the direction of your loop:
for (int i = answers.Count - 1; i >= 0; i--)
{
// ....
answers.RemoveAt(i);
}
This will still process all of the items in the list and leave you with nothing in the list at the end.
I would like to create a for loop to check if an index value has repeated, and if it has to remove it from the original and display an updated list with no repeated index values.
I have and Array (called Original) with multiple values being repeated, and then I created a Temporary Array (called TempArray) with the same exact values.
I want to check the Original and TempArray values against each other to see if there are duplicates.
I want my code to be similar to a previous one I did where I deleted an index from the middle of my array, as follows
for (int i = 0; i < Original.Length; i++)
{
TempArray[i] = Original[i];
}
Original = new int[Original.Length - 1];
//Set index to delete
int DeleteIndex = 3;
//modify size of Orignial array and copy in array without deleted element index
for (int i = 0; i < TempArray.Length; i++)
{
if (i < DeleteIndex)
{
Original[i] = TempArray[i];
}
else if (i > DeleteIndex)
{
Original[i - 1] = TempArray[i];
}
}
P.S. Original[] is an array from a text file. Sorry if my explanation is hard to understand as I am new to computer programming.
Also is there any way to do this code without LINQ, I have to create using arrays only as its all thats been taught at school?
It took some time to understand what you want :)
to check if an index value has repeated, and if it has to remove it from the original and display an updated list with no repeated index values
It is shortly called distinct values. There is a LINQ method .Distinct():
Original = Original.Distinct().ToArray();
It will remove all repeated values.
where I deleted an index from the middle of my array
You can do this easier by converting to List, applying RemoveAt and back:
var list = new List<int>(Original);
list.RemoveAt(DeleteIndex);
Original = list.ToArray();
P.S. Assuming that you say "index" about the values in your array, it is pretty confusing. Array does not store indices - index is usually understood as a key of an array.
May be this will do the trick for you. I am assuming that you need to remove duplicate from your array
Original = Original.Distinct().ToArray();
Will Returns distinct elements from a sequence by using the default equality comparer to compare values.
I have an array that are having some different values. one array called saveforRR this should work like whenever i have any value that less that 0, it will be removed from the array. Also, the values in the array must reduced by 1. I do not know how many iterations are going to take to make my array Length =0. so I used while loop. However, when i run the code my loop stops in this line fortheaddingvalue = (int)saveforRR[w]; //It says her that my array is out from boundaries, which i do not know how? How can I fix this problem? can you advise me please?
//Create variables and set up the arrays
int value = 7;
int [] saveforRR = {1,2,3,4,5,15,86};
//start get the values reduced
int fortheaddingvalue;
int w = 0;
//Run the while loop to reduce the value in the saveforRR array.
while(saveforRRName.Length !=0 && saveforRR.Length !=0)
{
fortheaddingvalue = (int)saveforRR[w]; //It says her that my array is out from boundaries, which i do not know how?
fortheaddingvalue = fortheaddingvalue - 1;
if (fortheaddingvalue > 0)
{
saveforRR[w] = fortheaddingvalue;
txtOutput.Text += "\r\n" +saveforRR[w] + " this is the value";
}
else
{
Array.Clear(saveforRR, w, 1);
txtOutput.Text += "\r\n" + saveforRR[w] + "this is the value Remover";
}
w++;
}
The length of your array will never be zero. The Clear method doesn't remove items from the array.
An array can't be resized. You can use the Resize method to get the same effect, as that will create a new array with a different size, and copy the items to it. That's however not efficient, you should use a List<int> instead, as that supports actual resizing.
It seems that nobody mentioned the break-statement. You can use it break out of any loop:
while(true)
{
// Eternal loop here...
// Break out
break;
}
Read more about it here: break
Other ways to exit loop include for example goto, return or setting the loop expression not to match