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Generate random sequence of AlphaNumeric [closed]

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I want a code to generate sequence of Alphanumeric character like LLNNLLNNLL where L is the Letter and N is the number. For example if the length is 5 the sequence will be LLNNL and if the length is 6 the sequence will be LLNNLL and if 7 it would be LLNNLLN.
string alphabets = "ABCDEFGHIJKLMNPQRSTUVWX";
int length = model.VALUE_INT;
string result = "";
for (int i = 0; i < length; i++)
{
int next = _random.Next(23);
result += alphabets.ElementAt(next);
result += _randomNum.Next(1, 9);
}
This is what I have tried but condition is not fulfilling

For each position (value of i) of your output string you need to check if you need a character or an integer.
Since the pattern repeats every 4 positions, you can achieve this using the modulo operator:
for (int i = 0; i < length; i++)
{
switch (i % 4)
{
case 0:
case 1:
int next = _random.Next(23);
result += alphabets.ElementAt(next);
break;
case 2:
case 3:
result += _randomNum.Next(1, 9);
break;
}
}
Or another possibility: Add blocks of LLNN and then truncate the result to the needed length...
for (int i = 0; i <= (length/4); i++)
{
result += alphabets.ElementAt(_random.Next(23));
result += alphabets.ElementAt(_random.Next(23));
result += _randomNum.Next(1, 9);
result += _randomNum.Next(1, 9);
}
result = result.Substring(0,length);
If you want to improve these lines, you can use a StringBuilder

How to make only chosen characters uppercase in C# [closed]

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I want to make every other letter uppercase, how do I do that?
Code:
String a = ("aábdeéðfghiíjklmnoóprstuúvxyýþæö");
for (int i=0; i < a.Length; i++)
{
Console.Write(a.ToUpper()[i]+ ",");
}

Using Linq:
string a = "aábdeéðfghiíjklmnoóprstuúvxyýþæö";
var converted =
new string(a.Select((ch, i) => ((i % 2) == 0) ? ch : Char.ToUpper(ch)).ToArray());
Console.WriteLine(converted);

Increment your loop by 2.
Example:
String a = ("aábdeéðfghiíjklmnoóprstuúvxyýþæö");
for (int i=0; i<a.Length; i+=2)
Console.Write(a.ToUpper()[i]+ ",");
For every even alphabet start loop from 0 and for odd start from 1.

Linq answer is very good and has the advantage to be one liner, but a normal loop here is twice faster than the Linq solution
char[] a = "aábdeéðfghiíjklmnoóprstuúvxyýþæö".ToCharArray();
for (int i = 0; i < a.Length; i++)
{
if (i % 2 != 0)
{
a[i] = Char.ToUpper(a[i]);
}
}
string result = new string(a);

Using LINQ to go through each char in the string. If it is divisible by 2 then that means its every other letter. So make that upper case, if not divisible by 2 then leave it as it is. Rejoin all the chars together in an array then convert that back into a string.
String a = ("aábdeéðfghiíjklmnoóprstuúvxyýþæö");
var convertedString = new string(a
.Select((c, i) => (i + 1) % 2 == 0 ? Char.ToUpper(c) : c)
.ToArray());

String a = ("aábdeéðfghiíjklmnoóprstuúvxyýþæö");
for (int i=0; i<a.Length; i++)
{
if (i % 2 == 0)
{
a = a.Substring(0, i) + a.Substring(i, 1).ToUpper() + a.Substring(i);
}
}
The % symbol is modulo, in this context if the index if divisible by 2 make the symbol upper case.
EDIT: as correctly pointed out, string are immutable, I've edited appropriately. This most likely isn't the most efficient way of doing this, I'd recommend using LINQ for a more efficient algorithm

You can use Linq.
string oldString = "aábdeéðfghiíjklmnoóprstuúvxyýþæö";
string alternatedString = string.Concat(
oldString.ToLower().Select((character, index) => index % 2 == 0 ? character : char.ToUpper(character)));
Output: aÁbDeÉðFgHiÍjKlMnOóPrStUúVxYýÞæÖ
Or
string oldString = "aábdeéðfghiíjklmnoóprstuúvxyýþæö";
StringBuilder alternatedString = new StringBuilder();
for(int index=0; index<oldString.Length; index++)
{
if(index % 2 == 0)
alternatedString.Append(oldString[index].ToString().ToLower());
else
alternatedString.Append(oldString[index].ToString().ToUpper());
}
Output: aÁbDeÉðFgHiÍjKlMnOóPrStUúVxYýÞæÖ

Change from iterative to recursive method [closed]

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int arraySum (int [] a, int n)
{
int sum = 0;
n = a.size();
for (int i = 1; i < n; i++)
sum += a[i];
return sum;
}
I want to convert this code from iterative to recursive.

C# Version:
int arraySum ( int [] a, int sum = 0, int i = 0 ) /*i = 0, technically means this code is logically different from yours, however it will count every element and is just a default :)*/
{
if( i < a.Length )
return arraySum( a, sum + a[i], ++i );
return sum;
}

You need:
1- Recursive definition like: sum(n) = n + sum(n-1)
2- You need to specify where should you stop so the recursion does not last forever.
for example: if (n == 0) return 0;
based on this you can code at any language.
C++ Example:
int arraySum (int a[], int n)
{
if(n==1)
return a[n-1];
else
return a[n-1] + arraySum (a, n-1);
}

How to Zip two numbers using c# [closed]

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string A = "1234"
string B = "567890"
I want to zip the numbers. Out put should display as "1526374890"
what is the best way to achieve this using C# code.

You can do that with the following code. It does not make any assumptions about which string is longer.
string A = "1234";
string B = "567890";
char[] chars = new char[A.Length + B.Length];
int charsIndex = 0;
for (int i = 0; i < A.Length || i < B.Length; i++)
{
if(i < A.Length)
chars[charsIndex++] = A[i];
if(i < B.Length)
chars[charsIndex++] = B[i];
}
string result = new string(chars);
Console.WriteLine(result);

Logic to generate an alphabetical sequence in C# [closed]

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The sequence should go like this.
A-Z,AA-AZ,BA-BZ,CA-CZ,.......,ZA-ZZ
After ZZ it should start from AAA.
Then AAA to ZZZ and then AAAA to ZZZZ and so on.
This sequence is pretty much like that of an Excel sheet.
Edit: Added my code
private void SequenceGenerator()
{
var numAlpha = new Regex("(?<Numeric>[0-9]*)(?<Alpha>[a-zA-Z]*)");
var match = numAlpha.Match(txtBNo.Text);
var alpha = match.Groups["Alpha"].Value;
var num = Convert.ToInt32(match.Groups["Numeric"].Value);
lastChar = alpha.Substring(alpha.Length - 1);
if (lastChar=="Z")
{
lastChar = "A";
txtBNo.Text = num.ToString() + "A" + alpha.Substring(0, alpha.Length - 1) + lastChar;
}
else
{
txtBNo.Text = num.ToString() + alpha.Substring(0, alpha.Length - 1) + Convert.ToChar(Convert.ToInt32(Convert.ToChar(lastChar)) + 1);
}
}
This is what I've done. But, I know that is a wrong logic.
Thanks.

As I've wrote in the comment, it's a base-conversion problem, where your output is in base-26, with symbols A-Z
static string NumToLetters(int num)
{
string str = string.Empty;
// We need to do at least a "round" of division
// to handle num == 0
do
{
// We have to "prepend" the new digit
str = (char)('A' + (num % 26)) + str;
num /= 26;
}
while (num != 0);
return str;
}

Lucky for you, I've done this once before. the problems I've encountered is that in the Excel sheet there is no 0, not even in double 'digit' 'numbers'. meaning you start with a (that's 1) and then from z (that's 26) you go straight to aa (27). This is why is't not a simple base conversion problem, and you need some extra code to handle this.
Testing the function suggested by xanatos results with the following:
NumToLetters(0) --> A
NumToLetters(25) --> Z
NumToLetters(26) --> BA
My solution has more code but it has been tested against Excel and is fully compatible, except it starts with 0 and not 1, meaning that a is 0, z is 25, aa is 26, zz 701, aaa is 702 and so on). you can change it to start from 1 if you want, it's fairly easy.
private static string mColumnLetters = "zabcdefghijklmnopqrstuvwxyz";
// Convert Column name to 0 based index
public static int ColumnIndexByName(string ColumnName)
{
string CurrentLetter;
int ColumnIndex, LetterValue, ColumnNameLength;
ColumnIndex = -1; // A is the first column, but for calculation it's number is 1 and not 0. however, Index is alsways zero-based.
ColumnNameLength = ColumnName.Length;
for (int i = 0; i < ColumnNameLength; i++)
{
CurrentLetter = ColumnName.Substring(i, 1).ToLower();
LetterValue = mColumnLetters.IndexOf(CurrentLetter);
ColumnIndex += LetterValue * (int)Math.Pow(26, (ColumnNameLength - (i + 1)));
}
return ColumnIndex;
}
// Convert 0 based index to Column name
public static string ColumnNameByIndex(int ColumnIndex)
{
int ModOf26, Subtract;
StringBuilder NumberInLetters = new StringBuilder();
ColumnIndex += 1; // A is the first column, but for calculation it's number is 1 and not 0. however, Index is alsways zero-based.
while (ColumnIndex > 0)
{
if (ColumnIndex <= 26)
{
ModOf26 = ColumnIndex;
NumberInLetters.Insert(0, mColumnLetters.Substring(ModOf26, 1));
ColumnIndex = 0;
}
else
{
ModOf26 = ColumnIndex % 26;
Subtract = (ModOf26 == 0) ? 26 : ModOf26;
ColumnIndex = (ColumnIndex - Subtract) / 26;
NumberInLetters.Insert(0, mColumnLetters.Substring(ModOf26, 1));
}
}
return NumberInLetters.ToString().ToUpper();
}

Try this method:
public static IEnumerable<string> GenerateItems()
{
var buffer = new[] { '#' };
var maxIdx = 0;
while(true)
{
var i = maxIdx;
while (true)
{
if (buffer[i] < 'Z')
{
buffer[i]++;
break;
}
if (i == 0)
{
buffer = Enumerable.Range(0, ++maxIdx + 1).Select(c => 'A').ToArray();
break;
}
buffer[i] = 'A';
i--;
}
yield return new string(buffer);
}
// ReSharper disable once FunctionNeverReturns
}
This is infinite generator of alphabetical sequence you need, you must restrict count of items like this:
var sequence = GenerateItems().Take(10000).ToArray();
Do not call it like this (it cause infinite loop):
foreach (var i in GenerateItems())
Console.WriteLine(i);