Develop Reference

Dividing a decoded value, not minus/removing the last digit

I have a method where I decode some information from a file, when I attempt to divide the value decoded by 10, let's say, it removes the last digit.
private int DecodeInt(byte[] bytes, int start)
{
int r2 = 0;
byte ch1 = bytes[start];
byte ch2 = bytes[start + 1];
int result = ch2 + (ch1 * 256);
if (result > 32767)
{
r2 = 0;
}
else
{
r2 = result;
}
return r2;
}
I know the value displayed should be 39.5.
Label_1.Text = (DecodeInt(Rec, 22)).ToString(); // Displays 395
Label_1.Text = (DecodeInt(Rec, 22) / 10).ToString(); // Displays 39
I'm confused as to why it doesn't function... I'm sure it will be simple adjustment but it's driving me a little mad.

You are dividing an int with an int so result will be in int only. What you can do is :
Label_1.Text = (DecodeInt(Rec, 22) / 10.0).ToString();

I looked here for my solution: https://stackoverflow.com/a/661042/2952390
double result = (double)DecodeInt(Rec,20)/(double)10;
Much easier than I thought, of course.

Split number into groups of 3 digits

I want to make a method that takes a variable of type int or long and returns an array of ints or longs, with each array item being a group of 3 digits. For example:
int[] i = splitNumber(100000);
// Outputs { 100, 000 }
int[] j = splitNumber(12345);
// Outputs { 12, 345 }
int[] k = splitNumber(12345678);
// Outputs { 12, 345, 678 }
// Et cetera
I know how to get the last n digits of a number using the modulo operator, but I have no idea how to get the first n digits, which is the only way to make this method that I can think of. Help please!

Without converting to string:
int[] splitNumber(int value)
{
Stack<int> q = new Stack<int>();
do
{
q.Push(value%1000);
value /= 1000;
} while (value>0);
return q.ToArray();
}
This is simple integer arithmetic; first take the modulo to get the right-most decimals, then divide to throw away the decimals you already added. I used the Stack to avoid reversing a list.
Edit: Using log to get the length was suggested in the comments. It could make for slightly shorter code, but in my opinion it is not better code, because the intent is less clear when reading it. Also, it might be less performant due to the extra Math function calls. Anyways; here it is:
int[] splitNumber(int value)
{
int length = (int) (1 + Math.Log(value, 1000));
var result = from n in Enumerable.Range(1,length)
select ((int)(value / Math.Pow(1000,length-n))) % 1000;
return result.ToArray();
}

By converting into a string and then into int array
int number = 1000000;
string parts = number.ToString("N0", new NumberFormatInfo()
{
NumberGroupSizes = new[] { 3 },
NumberGroupSeparator = "."
});
By using Maths,
public static int[] splitNumberIntoGroupOfDigits(int number)
{
var numberOfDigits = Math.Floor(Math.Log10(number) + 1); // compute number of digits
var intArray = new int[Convert.ToInt32(numberOfDigits / 3)]; // we know the size of array
var lastIndex = intArray.Length -1; // start filling array from the end
while (number != 0)
{
var lastSet = number % 1000;
number = number / 1000;
if (lastSet == 0)
{
intArray[lastIndex] = 0; // set of zeros
--lastIndex;
}
else if (number == 0)
{
intArray[lastIndex] = lastSet; // this could be your last set
--lastIndex;
}
else
{
intArray[lastIndex] = lastSet;
--lastIndex;
}
}
return intArray;
}

Try converting it to string first and do the parsing then convert it back to number again

Convert to string
Get length
If length modulus 3 == 0
String substring it into ints every 3
else if
Find remainder such as one or two left over
Substring remainder off of front of string
Then substring by 3 for the rest

You can first find out how large the number is, then use division to get the first digits, and modulo to keep the rest:
int number = 12345678;
int len = 1;
int div = 1;
while (number >= div * 1000) {
len++;
div *= 1000;
}
int[] result = new int[len];
for (int i = 0; i < result.Length; i++) {
result[i] = number / div;
number %= div;
div /= 1000;
}

You can use this with the System.Linq namespace from .NET 3.5 and above:
int[] splitNumber(long value)
{
LinkedList<int> results = new LinkedList<int>();
do
{
int current = (int) (value % 1000);
results.AddFirst(current);
value /= 1000;
} while (value > 0);
return results.ToArray();// Extension method
}
I use LinkedList<int> to avoid having to Reverse a list before returning. You could also use Stack<int> for the same purpose, which would only require .NET 2.0:
int[] splitNumber(long value)
{
Stack<int> results = new Stack<int>();
do
{
int current = (int) (value % 1000);
results.Push(current);
value /= 1000;
} while (value > 0);
return results.ToArray();
}

How to get the maximum number of a particular length

I have a number, for example 1234567897865; how do I max it out and create 99999999999999 ?
I did this this way:
int len = ItemNo.ToString().Length;
String maxNumString = "";
for (int i = 0; i < len; i++)
{
maxNumString += "9";
}
long maxNumber = long.Parse(maxNumString);
what would be the better, proper and shorter way to approach this task?

var x = 1234567897865;
return Math.Pow(10, Math.Ceiling(Math.Log10(x+1e-6))) - 1;
To expand on comments below, if this problem was expressed in hex or binary, it could be done very simply using shift operators
i.e., "I have a number, in hex,, for example 3A67FD5C; how do I max it out and create FFFFFFFF?"
I'd have to play with this to make sure it works exactly, but it would be something like this:
var x = 0x3A67FD5C;
var p = 0;
while((x=x>>1)>0) p++; // count how many binary values are in the number
return (1L << 4*(1+p/4)) - 1; // using left shift, generate 2 to
// that power and subtract one

long maxNumber = long.Parse(new String('9', ItemNo.ToString().Length));

Try this:
int v = 1;
do {
v = v * 10;
} while (v <= number);
return v - 1;

int numDigits = (int)Math.Ceiling(Math.Log10(number));
int result = (int)(Math.Pow(10, numDigits) - 1)
I don't have a compiler available at the moment, so some additional string/double conversions may need to happen here.

need a better way add leading digits to int and return array of digits

I need to create a modulus check which adds leading digits, lets say 0, to a seed int. I then need to return an array of digits in the array as I need to do a calculation on each digit to return a new whole number.
my code is as follows,
var seed = 1234;
var seedString = seed.ToString();
var test = new List<int>();
for(int i = 0; i < 10 - seedString.Length; i++)
{
test.Add(0);
}
var value = seed;
for(int i = 0; i < seedString.Length; i ++)
{
test.Insert(10 - seedString.Length, value % 10);
value = value / 10;
}
is there an easier way of doing this?

If you want to convert your number to a 10-digit string, you can format the number using a Custom Numeric Format String as follows:
string result = seed.ToString("0000000000");
// result == "0000001234"
See: The "0" Custom Specifier
If you need a 10-element array consisting of the individual digits, try this:
int[] result = new int[10];
for (int value = seed, i = result.Length; value != 0; value /= 10)
{
result[--i] = value % 10;
}
// result == new int[] { 0, 0, 0, 0, 0, 0, 1, 2, 3, 4 }
See also: Fastest way to separate the digits of an int into an array in .NET?

Try this:
int myNumber = 1234;
string myStringNumber = myNumber.ToString().PadLeft(10, '0');
HTH

Another shorthand way of getting the string representation would be
int num = 1234;
num.ToString("D10");

C# Number to BitMask32 to Values

I am getting a number such as 513. I need to convert this number to a bitmask32 then I need to count where each 1 bit is in the array
For Example
513 = 0 and 9
How would I go about converting the number to a bit32 then reading the values?
Right now I am just converting the number to a string binary value:
string bit = Convert.ToString(513, 2);
Would there be a more effective way to do this? How would I convert the value to a bit array?
Thanks

var val = 513;
for(var pos=0;;pos++)
{
var x = 1 << pos;
if(x > val) break;
if((val & x) == x)
{
Console.WriteLine(pos);
}
}

The BitVector32 class is an utility class that can help you out for this, if you really want to keep a bit map.

using System.Collections;
int originalInt = 7;
byte[] bytes = BitConverter.GetBytes(originalInt);
BitArray bits = new BitArray(bytes);
int ndx = 9; //or whatever ndx you actually care about
if (bits[ndx] == true)
{
Console.WriteLine("Bit at index {0} is on!", ndx);
}

To test bit #i in number n:
if ((n & (1 << i)) != 0)