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How do I copy the array elements and also reversing certain elements with Array.Copy() in c#?

Elements of SourceArray are being copied to 2 separate Arrays namely DestArray1 and DestArray2.
output:
DestArray1 will have the first 4 elements of SourceArray but in the reverse form [4 3 2 1]
DestArray2 will have the last 4 elements of SourceArray. [5 6 7 8]
I want to replace the for loop with Array.Copy() method
if not reversed then Array.Copy() works kind of fine except for the last element, but to copy with reverse, it seems the Array.Copy doesn't work or I am not able to implement it.
int i, j;
int bytelength =8;
int halfbytelength = 4;
byte[] SourceArray = new byte[]{ 1, 2, 3, 4, 5, 6, 7, 8 };
byte[] DestArray1 = new byte[4];
byte[] DestArray2 = new byte[4];
for (i = halfbytelength - 1, j = 0; i >= 0; i -= 1, j++)
{
DestArray1[j] = SourceArray[i];
}
for (i = halfbytelength; i < bytelength; i += 1)
{
DestArray2[i - halfbytelength] = SourceArray[i];
}
I tried following the code but the results are not as expected as seen in(Results:), is there a way to do it?
Array.Copy(SourceArray, 0, DestArray1, 3, 0);
Array.Copy(SourceArray, 4, DestArray2, 0, 3);
Result:
DestArray1: [0 0 0 0]
DestArray2: [5 6 7 0]

First array.
To reverse array you can just call Array.Reverse() after copying:
Array.Copy(SourceArray, 0, DestArray1, 0, 4);
Array.Reverse(DestArray1);
Second array.
if not reversed then Array.Copy() works kind of fine except for the
last element
Because you pass invalid count of elements to copy (last parameter):
Array.Copy(SourceArray, 4, DestArray2, 0, 3); // 3 - elements count, not an index
Simply replace 3 with 4:
Array.Copy(SourceArray, 4, DestArray2, 0, 4); // 4 and it will copy including the last element

C# locate value in a array and move it to right

My task is to find a element in the array that is the same as given value, and then take it to right while maintaining the order of other elements. An example (Test Case):
{1, 2, 0, 1, 0, 1, 0, 3, 0, 1} for value = 0 => {1, 2, 1, 1, 3, 1, 0, 0, 0, 0}
While my code could do that above example, what it could not do is a very specific case: if the element in array equals value and the next element also equals value it will not shift the element. Again a example:
{ 1, int.MinValue, int.MinValue, int.MaxValue, int.MinValue, -1, -3, -9, 1 }, value = int.MinValue
Expected result: { 1, int.MaxValue, -1, -3, -9, 1, int.MinValue, int.MinValue, int.MinValue }
Result with my code: { 1, int.MinValue ,int.MaxValue, -1, -3, -9, 1, int.MinValue, int.MinValue }
I thought shifting is the one solution, is it? I am having a lot of problems with it, I also tried Array.Copy but there were problems the result was always out of range.
How can I make it so that it will shifts/rotates correctly in all cases?
Code:
static void Main(string[] args)
{
int[] source = new int[] { 1, int.MinValue, int.MinValue, int.MaxValue, int.MinValue, -1, -3, -9, 1 };
int value = int.MinValue;
for (int i = 0; i < source.Length; i++)
{
if (source[i] == value)
{
LeftShiftArray(source, i);
}
}
for (int i = 0; i < source.Length; i++)
{
Console.WriteLine(source[i]);
}
}
public static void LeftShiftArray(int[] source, int i)
{
var temp1 = source[i];
for (var j = i; j < source.Length - 1; j++)
{
source[j] = source[j + 1];
}
source[source.Length - 1] = temp1;
}
Now this

I have a simple approach to solve this problem. Run a loop, You keep on counting the numbers which are not equal to your number. And keep assigning to arr[count]. Then increment the count. And then finally you will be left to assign all the remaining numbers with the given number.
static void MoveToEnd(int []arr, int n)
{
int count = 0;
    for (int i = 0; i < arr.Length; i++)
        if (arr[i] != n)
         arr[count++] = arr[i];
    while (count < arr.Length)
        arr[count++] = n;
}
Please note I have typed this answer from phone, so please avoid typing mistakes.

This is a classic off by one error. Think about it like this:
Let's say you are moving all 0s to the back (value = 0). When you find a zero at some position, let's say source[2], you turn your array from this:
1 1 0 0 1 1
source[2] ^
To this:
1 1 0 1 1 0
source[2] ^
Now that you've shifted the array, the next step in your code is to increase i by 1. That means the next comparison you make will be with source[3]. In the above array, that looks like this:
1 1 0 1 1 0
source[3] ^
Do you see the problem? Let me know if not and I can explain further.
PS. There are a couple of issues with the other code that was posted that will probably stop you from getting full points if you were to turn it in for an assignment :)

IndexError in array PYTHON

I am tring to write this C# function in Python, unfortunatly I have this ERROR: IndexError: list assignment index out of range in Population.BinaryX.insert([i][j], dec) line. Can anyone tell me how can I fix this problem?! What`s wrong I did?
C# CODE:
public class Population
{
public float[] CodedX = new float[20];
public float[,] BinaryX = new float[10, 8];
}
private void BinaryTranslating()
{
int dec;
int j = 0;
for (var i = 0; i < 10; i++)
{
while (Population.CodedX[i] > 1 & j < 8)
{
dec = (int)Population.CodedX[i] % 2;
Population.BinaryX[i, j] = dec;
Population.CodedX[i] /= 2;
j++;
}
j = 0;
}
}
private void DecimalTranslating()
{
for (var i = 0; i < 10; i++)
{
Population.CodedX[i] = Population.BinaryX[i, 7] * 128 + Population.BinaryX[i, 6] * 64 +
Population.BinaryX[i, 5] * 32 + Population.BinaryX[i, 4] * 16 +
Population.BinaryX[i, 3] * 8 + Population.BinaryX[i, 2] * 4 +
Population.BinaryX[i, 1] * 2 + Population.BinaryX[i, 0];
}
}
Python CODE:
class Population:
CodedX = []
BinaryX = [[], []]
class Application:
#staticmethod
def binary_translating():
j = 0
for i in range(10):
while Population.CodedX[i] > 1 & j < 8:
dec = int(Population.CodedX[i]) % 2
Population.BinaryX.insert([i][j], dec)
Population.CodedX[i] /= 2
j += 1
j = 0
#staticmethod
def decimal_translating():
for i in range(10):
new_item = Population.BinaryX[i][7] * 128 + Population.BinaryX[i][6] * 64 + Population.BinaryX[i][5] * 32 +\
Population.BinaryX[i][4] * 16 + Population.BinaryX[i][3] * 8 + Population.BinaryX[i][2] * 4 +\
Population.BinaryX[i][1] * 2 + Population.BinaryX[i][0]
Population.CodedX.insert(i, new_item)

Consider the [i][j] expression in Population.BinaryX.insert([i][j], dec). That expression creates a 1 item list containing the value of i and then tries to take the jth item from that list.
>>> i=1
>>> j=2
>>> [i][j]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: list index out of range
Python lists are one dimensional and if you want a multidimensional list, you need to create a list of lists or use some other structure such as a numpy or pandas array.
One option is to preallocate the array with a known value so that you can simply index it later
#staticmethod
def binary_translating():
Population.BinaryX = [[None] * 8 for _ in range(10)]
j = 0
for i in range(10):
while Population.CodedX[i] > 1 & j < 8:
dec = int(Population.CodedX[i]) % 2
Population.BinaryX[i][j] = dec
Population.CodedX[i] /= 2
j += 1
j = 0
Another option is to insert into the sublist:
#staticmethod
def binary_translating():
Population.BinaryX = []
j = 0
for i in range(10):
Population.BinaryX.insert([])
while Population.CodedX[i] > 1 & j < 8:
dec = int(Population.CodedX[i]) % 2
Population.BinaryX[i].insert(j, dec)
Population.CodedX[i] /= 2
j += 1
j = 0

please make sure that Population.BinaryX is a valid entity and has at least 10 element in it because you are running the loop 10 times. Same goes for CodedX.
If either of them do not have at least 10 elements, you will get
IndexError: list assignment index out of range
Try..
class Population:
CodedX = [0 for i in range(10)]
BinaryX = [[0 for i in range(10)] for j in range(10)]
This is preallocating as mentioned by tdelaney.
If you look at each functions in the Application class, they try to use either BinaryX or CodedX arrays but if these arrays do not have any elements in them, then how will python index into them?
What I mean is before calling the decimal_translating() function, the Population.BinrayX must have elements in it. It cannot be empty array.
Similarly, before calling the binary_translating() function, Population.CodedX must have elements in it.
[edit #1]
After your comments and trying to understand your code.Here is what I have:-
class Population(object):
def __init__(self):
self.CodedX = [0 for i in range(10)] # as per your C# code
self.BinaryX = []
# debug code to fill CodedX array - remove it
for i in range(10):
self.CodedX[i] = int(761)
def binary_translating(self):
for i in range(10):
j = 0
self.BinaryX.append([0 for k in range(10)])
while (self.CodedX[i] > 0) and (j < 10):
dec = int(self.CodedX[i] % 2)
self.BinaryX[i][j] = dec # this will append at j
self.CodedX[i] = int(self.CodedX[i] / 2)
j += 1
# debug code to print - remove it
print(self.BinaryX)
# debug code to clear CodedX - remove it
for i in range(10):
self.CodedX[i] = int(0)
def decimal_translating(self):
for i in range(10):
value = self.BinaryX[i][7] * 128 + self.BinaryX[i][6] * 64 + self.BinaryX[i][5] * 32 + \
self.BinaryX[i][4] * 16 + self.BinaryX[i][3] * 8 + self.BinaryX[i][2] * 4 + \
self.BinaryX[i][1] * 2 + self.BinaryX[i][0]
self.CodedX[i] = value
print(self.CodedX)
pop = Population()
pop.binary_translating()
pop.decimal_translating()
I have added some debug code to have some starting values in CodedX and print statements for you to see the output.
generates the output:
[[1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1], [1, 0, 0, 1, 1, 1, 1, 1, 0, 1]]
[249, 249, 249, 249, 249, 249, 249, 249, 249, 249]
[edit #2]

How to incrementally iterate through all possible values of a byte array of size n?

For my question n=16, but a generic answer would be appreciated too.
So I have a byte array:
byte[] key;
My problem is that I want to iterate through all possible values of each element in this array, combined. I know this will take ages, and I'm not looking to actually complete this loop, just to make a loop which will at least attempt this.
So e.g.:
First iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
}
Second iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
}
Third iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
}
Final iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255};
}
Obviously I have just hardcoded the array above. I need a way of doing this in a proper way. Again, I know there are many different combinations. All I need is a way to start iterating through all possible values. How can I do this in my loop?
I.e. what should I replace the body of my loop with, in order to iterate through all possible values of a byte array of size 16.
What I have tried:
In the body of the loop I have tried the following:
key = new byte[16] { (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i };
Obviously wrong, will only test a small subset of possible values. Will just try i= 0,...,255 and then start over for when i=256 --> (byte)i = 0.
I suspect I need some more nesting. Possibly up to 16 nested loops, which sounds insane and probably wrong? I can't get my head around this problem, any help would be much appreciated!
Purpose:
The purpose of this question is to demonstrate how inefficient brute force cryptanalysis is in practice. The rest of my program works, I'm just stuck in this loop.

In case you don't realize: 16 bytes is the size of a Guid or the size of a standard cryptographic key size. There are so many combinations that you cannot enumerate even a fraction. Maybe you can enumerate the last 8 bytes if you parallelize across 1000 machines and wait a year.
You could do that easily by running a for loop from 0 to ulong.MaxValue. I'm submitting this as an answer because this very simple idea allows you to start enumerating and essentially never come to a point where you finish.
for (ulong i = 0; i < ulong.MaxValue; i++) {
var bytes = new [] {
0, 0, 0, 0, 0, 0, 0, 0
, (byte)(i >> (7 * 8))
, (byte)(i >> (6 * 8))
, (byte)(i >> (5 * 8))
//...
, (byte)(i >> (0 * 8)) };
}
Or, just use 16 nested for loops. I don't think that's insane at all because it is so simple that it's clearly correct.

this is a sample code without any exception handling and kind of inefficient to simulate a counter like the one you mentioned
public static void NextIteration(byte[] input)
{
if (input.All(x => x == 255))
throw new InvalidOperationException("there is no iteration left");
var converted = input.Select(x => (int) x).ToArray();
converted[0]++;
for (var i = 0; i < converted.Length; i++)
{
if (converted[i] == 256)
{
converted[i] = 0;
converted[i + 1]++;
}
}
for (var i = 0; i < input.Length; i++)
{
input[i] = (byte) converted[i];
}
}

How to read a range of bytes from a bytearray in c#

I have to read a range of bytes from a byte array. I have the starting position and the ending position to read.
-(NSData *) getSubDataFrom:(int)stPos To:(int)endPos withData:(NSData *) data{
NSRange range = NSMakeRange(stPos, endPos);
return [data subDataWithRage:range];
}
The above code in ObjectiveC reads the range of data(bytes) from a NSData(byteArray). Is there any equivelent method in c# to do the same. or how else we can do this. Please advise!

What do you mean by read? Copy a range of bytes into another byte array?
var mainArray = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
var startPos = 5;
var endPos = 10;
var subset = new byte[endPos - startPos + 1];
Array.Copy(mainArray, startPos, subset, 0, endPos - startPos + 1);
From MSDN

Try the Array.Copy() or Array.CopyTo() method.