I found a curious effect in some code I wrote that I don't understand. I found a workaround but I'd like to know why the original code doesn't work as expected.
So populating a jagged array, I tried to define each cell individually. This resulted in 10 copies of the last array defined. From this code:
for (int i = 0; i < 10; i++)
{
serialisableHighScores.scores[i][0] = _highScores[i].date;
serialisableHighScores.scores[i][1] = _highScores[i].score;
serialisableHighScores.scores[i][2] = _highScores[i].questionsAsked;
}
Whereas when using a single dimension array as an intermediate, the data saved as expected. By which I mean there were 10 unique arrays saved in the jagged array. From this code:
for (int i = 0; i < 10; i++)
{
int[] scoreArray = { _highScores[i].date, _highScores[i].score, _highScores[i].questionsAsked };
serialisableHighScores.scores[i] = scoreArray;
}
The reason is that a jagged array is actually an array of arrays of values.
Since arrays are objects, reference types, it means that if you construct a jagged array with room for 10 arrays, all those array references are initialized to null.
In other words:
int[][] a = new int[10][];
a[0][0] = 10;
throws NullReferenceException.
The code can be thought of like this:
int[][] a = new int[10][];
int[] temp = a[0]; // this works, but temp is now null
temp[0] = 10; // throws NullReferenceException
Either you assign a fully populated array into the first slot, or you assign an initialized array without the values, like this:
for (int i = 0; i < 10; i++)
{
serialisableHighScores.scores[i] = new int[3];
serialisableHighScores.scores[i][0] = _highScores[i].date;
serialisableHighScores.scores[i][1] = _highScores[i].score;
serialisableHighScores.scores[i][2] = _highScores[i].questionsAsked;
}
Now, that's just the explanation of why it crashes on your end. The best option you have available is not to use arrays like this, that is, don't use 2-dimensional arrays to keep one list of related values, instead use objects:
public class Score
{
public Score(DateTime date, int score, int questionsAsked)
{
Date = date;
Score = score;
QuestionsAsked = questionsAsked;
}
public DateTime Date { get; }
public int Score { get; }
public int QuestionsAsked { get; }
}
Additionally, arrays are good for fixed size things but in general it's usually better to use lists:
var serializableHighScores = new List<Score>();
for (int i = 0; i < 10; i++)
{
serializableHighScores.Add(new Score(_highScores[i].date, _highScores[i].score, _highScores[i].questionsAsked));
}
Though given the name of your variable, if you need to adhere to some badly designed (my opinion) serializing format with arrays of arrays it's probably better to just stick with your code.
I have the following object[] array:
array[0] = obj_1;
array[1] = obj_2;
array[2] = obj_3;
array[3] = NULL;
array[4] = NULL;
And I need to insert another element between the array[1] and array[2] like this:
array[0] = obj_1;
array[1] = obj_2;
array[2] = obj_New;
array[3] = obj_3;
array[4] = NULL;
I can't use List before someone suggest. Any ideas of how can I do that?
There is no direct way. You need to move the elements first, and then set the value at desired index.
Below is sample snippet (without any array index checks)
void InsertItem(object[] array, int index, object val)
{
for(int i=index;i<array.Length;i++)
{
array[i] = array[i-1];
}
array[index] = val;
}
Do note that Array once created are allocated contigigous location, and are of fixed size. They cannot be arbitrary moved.
If you require various such operations, i would suggest linked list data structure.
From your post, it sounds like you want to pop the last item off the array and not the first one.
If so, like Tilak has suggested, the simplest way is to take/determine the index where the item has to be inserted and move the items from current position to the next subsequent position and finally add the new item in the given index. You would want to watch out for what happens if the array is already full, do you want to drop the last item or not?
We can optimize a bit in Tilak's code, by not overwriting the array[index] item twice, once in loop and once outside.
I will do it a bit different, I will start from end and go up, so you can avoid a temp variable.
void InsertItem(object[] array, int index, object val)
{
for(int i=array.Length - 1; i > index; i--)
{
array[i] = array[i-1];
}
array[index] = val;
}
Like others have already said, List or LinkedList will be a better choice.
I just needed a light to do it. I used Tilak's example as my base and I did the following code (With some more things like add in the end of the list and with a starting empty array):
object[] array = new object[0];
public void Insert(int index, object val)
{
Array.Resize(ref array, array.Length + 1);
if (index >= array.Length-1)
{
array[array.Length - 1] = val;
return;
}
for (int i = 0; i < array.Length; i++)
{
if (index == i)
{
for (int idx = array.Length; idx > index; idx--)
{
array[idx-1] = array[idx-2];
}
array[i] = val;
return;
}
}
}
It is completely functional and the Array.Resize activates every time that I insert something so that my array will always be with the exactly number of slots that I need.
What I'm doing wrong? What I'm trying to do is to add to existing array linesLat values but for next value to insert in linesLat is to take previous from array and summ stepLong. But at the end getting error.
static void Main(string[] args)
{
var stepLong = (10.6237 - 5.9216) / 1000;
var stepLat = (47.7245 - 45.7368) / 1000;
double[] linesLat = { 45.7368 };
double[] linesLong = { 5.9216 };
for (var i = 1; i <= 999; )
{
linesLat[i] = linesLat[i - 1] + stepLat; // throws an error
i++;
}
}
Additional information: Index was outside the bounds of the array.
You should really go back to basics.
Array as a limited size and it will be on the exact size you declare it to be.
In your case you allocated two arrays in the size of 1 (Due to explicit initialization).
double[] linesLat = { 45.7368 }; // Size 1
double[] linesLong = { 5.9216 }; // Size 1
Meaning you can't loop from [0, 999], when you will try to take the value from position 1 (Because C# arrays are zero based; The first element is in the 0 place and not 1) you will get a KABOOM meaning you will get an exception telling you, your index (probably 1) is outside of the legal array bounds.
Solution: You should change your solution to declare a bigger array as #i_a_joref suggested.
var linesLat = new double[1000];
linesLat[0] = 45.7368;
Additionally, your loop can be written more properly:
for (var i = 1; i < linesLat.Length; i++)
{
linesLat[i] = linesLat[i - 1] + stepLat;
}
Possible solution variation for your problem.
If the only goal is to get the sum of the last formula, than array is redundant.
double sumOfFormula = 45.7368;
for (var i = 0; i < 1000; i++) // Will run [0, 999] 1000 iterations
{
sumOfFormula += stepLat;
}
Console.WriteLine("Sum: ", sumOfFormula);
You declared linesLat as an array of size one. If you want to put 999+ elements in it, you need to declare a bigger array.
Your array has a lenght of 1, and you try to iterate up to 999.
You need to instanciate your array with a lengh of 999
double[] linesLat = new double[999];
Your array have size of 1 and in for loop you are trying to access indexes greater then array size.
Just change:
double[] linesLat = { 45.7368 };
to:
double[] linesLat = new double[1000];
linesLat[0] = 45.7368;
Hi i am working on Grade Calculation. My problem here is if the length of string array is longer that int array it works skipping the last 2 grades.
ex:
int[] unit = new int[] {1,-3,3,4};
string[] letter_grade = new string[] {"A", "B","B","W","D","F"};
but if length of int array longer than that of string array its not working its throwing error Index was outside the bounds of the array.
int[] unit = new int[] {1,-3,3,4,5,6,7};
string[] letter_grade = new string[] {"A", "B","B"};
so my question how do i make it work for both??
int length = unit.Length;
int no_units = length;
double totalGrade_Points = 0.0;
int totalno_units = 0;
totalGPA = 0;
for (int i = 0; i < unit.Length; i++)
{
entrygot = findGpaListentry(letter_grade[i]); //Index was outside the bounds of the array.
if (entrygot != null)
{
//some code calculation
}
}
For array indexing you must have starting and stopping condition defined very well. For accessing two arrays either they must be equal or they are compared under certain valid conditions. Have a look at this:
for(int i=0;i<unit.length;i++){
entrygot = findGpaListentry(letter_grade[i]);// only if letter_grade is valid under all values of i i.e unit.length
}
// either you have to check as if;
if(lenght_of_letter_grade < i-1)
//then access
entrygot = findGpaListentry(letter_grade[i]);
You can't just check if the array item is null, because you would be out of the bounds of the array and you will get an exception before the null check occurs.
I would check the length of the array on each iteration...
for (int i = 0; i < unit.Length; i++)
{
if (currentArray.Length < i - 1) { break; }
// other code...
}
I think in your case, the number of elements will never be large hence performance wont be an issue. So I think you should be using a List instead of an array. With an array you will have to be insert checks each time some logic changes or you add other functionalities.
foreach loop is best for your scenerio.
foreach (string s in letter_grade)
{
entrygot = findGpaListentry(s);
if (entrygot != null)
{
//some code calculation
}
}
Probably a really simple one this - I'm starting out with C# and need to add values to an array, for example:
int[] terms;
for(int runs = 0; runs < 400; runs++)
{
terms[] = runs;
}
For those who have used PHP, here's what I'm trying to do in C#:
$arr = array();
for ($i = 0; $i < 10; $i++) {
$arr[] = $i;
}
You can do this way -
int[] terms = new int[400];
for (int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
Alternatively, you can use Lists - the advantage with lists being, you don't need to know the array size when instantiating the list.
List<int> termsList = new List<int>();
for (int runs = 0; runs < 400; runs++)
{
termsList.Add(value);
}
// You can convert it back to an array if you would like to
int[] terms = termsList.ToArray();
Edit: a) for loops on List<T> are a bit more than 2 times cheaper than foreach loops on List<T>, b) Looping on array is around 2 times cheaper than looping on List<T>, c) looping on array using for is 5 times cheaper than looping on List<T> using foreach (which most of us do).
Using Linq's method Concat makes this simple
int[] array = new int[] { 3, 4 };
array = array.Concat(new int[] { 2 }).ToArray();
result
3,4,2
If you're writing in C# 3, you can do it with a one-liner:
int[] terms = Enumerable.Range(0, 400).ToArray();
This code snippet assumes that you have a using directive for System.Linq at the top of your file.
On the other hand, if you're looking for something that can be dynamically resized, as it appears is the case for PHP (I've never actually learned it), then you may want to use a List instead of an int[]. Here's what that code would look like:
List<int> terms = Enumerable.Range(0, 400).ToList();
Note, however, that you cannot simply add a 401st element by setting terms[400] to a value. You'd instead need to call Add() like this:
terms.Add(1337);
By 2019 you can use Append, Prepend using LinQ in just one line
using System.Linq;
and then in NET 6.0:
terms = terms.Append(21);
or versions lower than NET 6.0
terms = terms.Append(21).ToArray();
Answers on how to do it using an array are provided here.
However, C# has a very handy thing called System.Collections
Collections are fancy alternatives to using an array, though many of them use an array internally.
For example, C# has a collection called List that functions very similar to the PHP array.
using System.Collections.Generic;
// Create a List, and it can only contain integers.
List<int> list = new List<int>();
for (int i = 0; i < 400; i++)
{
list.Add(i);
}
Using a List as an intermediary is the easiest way, as others have described, but since your input is an array and you don't just want to keep the data in a List, I presume you might be concerned about performance.
The most efficient method is likely allocating a new array and then using Array.Copy or Array.CopyTo. This is not hard if you just want to add an item to the end of the list:
public static T[] Add<T>(this T[] target, T item)
{
if (target == null)
{
//TODO: Return null or throw ArgumentNullException;
}
T[] result = new T[target.Length + 1];
target.CopyTo(result, 0);
result[target.Length] = item;
return result;
}
I can also post code for an Insert extension method that takes a destination index as input, if desired. It's a little more complicated and uses the static method Array.Copy 1-2 times.
Based on the answer of Thracx (I don't have enough points to answer):
public static T[] Add<T>(this T[] target, params T[] items)
{
// Validate the parameters
if (target == null) {
target = new T[] { };
}
if (items== null) {
items = new T[] { };
}
// Join the arrays
T[] result = new T[target.Length + items.Length];
target.CopyTo(result, 0);
items.CopyTo(result, target.Length);
return result;
}
This allows to add more than just one item to the array, or just pass an array as a parameter to join two arrays.
You have to allocate the array first:
int [] terms = new int[400]; // allocate an array of 400 ints
for(int runs = 0; runs < terms.Length; runs++) // Use Length property rather than the 400 magic number again
{
terms[runs] = value;
}
int ArraySize = 400;
int[] terms = new int[ArraySize];
for(int runs = 0; runs < ArraySize; runs++)
{
terms[runs] = runs;
}
That would be how I'd code it.
C# arrays are fixed length and always indexed. Go with Motti's solution:
int [] terms = new int[400];
for(int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
Note that this array is a dense array, a contiguous block of 400 bytes where you can drop things. If you want a dynamically sized array, use a List<int>.
List<int> terms = new List<int>();
for(int runs = 0; runs < 400; runs ++)
{
terms.Add(runs);
}
Neither int[] nor List<int> is an associative array -- that would be a Dictionary<> in C#. Both arrays and lists are dense.
You can't just add an element to an array easily. You can set the element at a given position as fallen888 outlined, but I recommend to use a List<int> or a Collection<int> instead, and use ToArray() if you need it converted into an array.
If you really need an array the following is probly the simplest:
using System.Collections.Generic;
// Create a List, and it can only contain integers.
List<int> list = new List<int>();
for (int i = 0; i < 400; i++)
{
list.Add(i);
}
int [] terms = list.ToArray();
one approach is to fill an array via LINQ
if you want to fill an array with one element
you can simply write
string[] arrayToBeFilled;
arrayToBeFilled= arrayToBeFilled.Append("str").ToArray();
furthermore, If you want to fill an array with multiple elements you can use the
previous code in a loop
//the array you want to fill values in
string[] arrayToBeFilled;
//list of values that you want to fill inside an array
List<string> listToFill = new List<string> { "a1", "a2", "a3" };
//looping through list to start filling the array
foreach (string str in listToFill){
// here are the LINQ extensions
arrayToBeFilled= arrayToBeFilled.Append(str).ToArray();
}
Array Push Example
public void ArrayPush<T>(ref T[] table, object value)
{
Array.Resize(ref table, table.Length + 1); // Resizing the array for the cloned length (+-) (+1)
table.SetValue(value, table.Length - 1); // Setting the value for the new element
}
int[] terms = new int[10]; //create 10 empty index in array terms
//fill value = 400 for every index (run) in the array
//terms.Length is the total length of the array, it is equal to 10 in this case
for (int run = 0; run < terms.Length; run++)
{
terms[run] = 400;
}
//print value from each of the index
for (int run = 0; run < terms.Length; run++)
{
Console.WriteLine("Value in index {0}:\t{1}",run, terms[run]);
}
Console.ReadLine();
/*Output：
Value in index 0: 400
Value in index 1: 400
Value in index 2: 400
Value in index 3: 400
Value in index 4: 400
Value in index 5: 400
Value in index 6: 400
Value in index 7: 400
Value in index 8: 400
Value in index 9: 400
*/
If you don't know the size of the Array or already have an existing array that you are adding to. You can go about this in two ways. The first is using a generic List<T>:
To do this you will want convert the array to a var termsList = terms.ToList(); and use the Add method. Then when done use the var terms = termsList.ToArray(); method to convert back to an array.
var terms = default(int[]);
var termsList = terms == null ? new List<int>() : terms.ToList();
for(var i = 0; i < 400; i++)
termsList.Add(i);
terms = termsList.ToArray();
The second way is resizing the current array:
var terms = default(int[]);
for(var i = 0; i < 400; i++)
{
if(terms == null)
terms = new int[1];
else
Array.Resize<int>(ref terms, terms.Length + 1);
terms[terms.Length - 1] = i;
}
If you are using .NET 3.5 Array.Add(...);
Both of these will allow you to do it dynamically. If you will be adding lots of items then just use a List<T>. If it's just a couple of items then it will have better performance resizing the array. This is because you take more of a hit for creating the List<T> object.
Times in ticks:
3 items
Array Resize Time: 6
List Add Time: 16
400 items
Array Resize Time: 305
List Add Time: 20
I will add this for a another variant. I prefer this type of functional coding lines more.
Enumerable.Range(0, 400).Select(x => x).ToArray();
You can't do this directly. However, you can use Linq to do this:
List<int> termsLst=new List<int>();
for (int runs = 0; runs < 400; runs++)
{
termsLst.Add(runs);
}
int[] terms = termsLst.ToArray();
If the array terms wasn't empty in the beginning, you can convert it to List first then do your stuf. Like:
List<int> termsLst = terms.ToList();
for (int runs = 0; runs < 400; runs++)
{
termsLst.Add(runs);
}
terms = termsLst.ToArray();
Note: don't miss adding 'using System.Linq;' at the begaining of the file.
This seems like a lot less trouble to me:
var usageList = usageArray.ToList();
usageList.Add("newstuff");
usageArray = usageList.ToArray();
Just a different approach:
int runs = 0;
bool batting = true;
string scorecard;
while (batting = runs < 400)
scorecard += "!" + runs++;
return scorecard.Split("!");
int[] terms = new int[400];
for(int runs = 0; runs < 400; runs++)
{
terms[runs] = value;
}
static void Main(string[] args)
{
int[] arrayname = new int[5];/*arrayname is an array of 5 integer [5] mean in array [0],[1],[2],[3],[4],[5] because array starts with zero*/
int i, j;
/*initialize elements of array arrayname*/
for (i = 0; i < 5; i++)
{
arrayname[i] = i + 100;
}
/*output each array element value*/
for (j = 0; j < 5; j++)
{
Console.WriteLine("Element and output value [{0}]={1}",j,arrayname[j]);
}
Console.ReadKey();/*Obtains the next character or function key pressed by the user.
The pressed key is displayed in the console window.*/
}
/*arrayname is an array of 5 integer*/
int[] arrayname = new int[5];
int i, j;
/*initialize elements of array arrayname*/
for (i = 0; i < 5; i++)
{
arrayname[i] = i + 100;
}
To add the list values to string array using C# without using ToArray() method
List<string> list = new List<string>();
list.Add("one");
list.Add("two");
list.Add("three");
list.Add("four");
list.Add("five");
string[] values = new string[list.Count];//assigning the count for array
for(int i=0;i<list.Count;i++)
{
values[i] = list[i].ToString();
}
Output of the value array contains:
one
two
three
four
five
You can do this is with a list. here is how
List<string> info = new List<string>();
info.Add("finally worked");
and if you need to return this array do
return info.ToArray();
Here is one way how to deal with adding new numbers and strings to Array:
int[] ids = new int[10];
ids[0] = 1;
string[] names = new string[10];
do
{
for (int i = 0; i < names.Length; i++)
{
Console.WriteLine("Enter Name");
names[i] = Convert.ToString(Console.ReadLine());
Console.WriteLine($"The Name is: {names[i]}");
Console.WriteLine($"the index of name is: {i}");
Console.WriteLine("Enter ID");
ids[i] = Convert.ToInt32(Console.ReadLine());
Console.WriteLine($"The number is: {ids[i]}");
Console.WriteLine($"the index is: {i}");
}
} while (names.Length <= 10);