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Creating strings from a template by replacing placeholders by all permutations of an input set

I want to make a simple generator of strings.
User inputs a "template" for string. Template can have placeholders in any place in it.
Then he inputs possible characters that can fit into any placeholder in string.
How it should work:
INPUT:
a.b.
123
OUTPUT:
[
"a1b1", "a1b2", "a1b3",
"a2b1", "a2b2", "a2b3",
"a3b1", "a3b2", "a3b3"
]
I found some of my old python code, but i don't understand it at all.
I split the input string to array of strings and array of dots.
Then I tried to increment just dots and each time just concat those two arrays in the right way.
But I found a new trouble.
string[] splitted = kt_NonCur.Split('.'); // array of constant strings
char[] nch = new char[splitted.Length - 1]; // array of new chars (generated)
char lgc = goodLetters.Last( ); // last good char
for( int i = 0; i < nch.Length - 1; i++ ) // set up all nch to first letter
nch[i] = goodLetters[0];
while( nch.Last( ) != lgc ) { // until last nch is set to last good char
outputData.Add($"{concatsplit(splitted, nch)}"); // concatsplit(s,n) concatenates two arrays into string
nch[0] = up(nch[0]); // up(char) gets next character from goodLetters. If there is no next, it returns first letter.
if( nch[0] == goodLetters[0] ) {
nch[1] = up(nch[1]);
if(nch[1] == goodLetters[0]){
nch[2] = up(nch[2]);
// .
// .
// .
}
}
}
And the problem is: I am facing a dilemma. Either find better way, or limit number of placeholders so that the code ladder is not too long. Of course I would add then some code that checks if it is the last and stop executing code for others, but I still would have to make

You can look at your problem this way: if you have P placeholders in your input string and the number of replacement characters is R, to construct every possibe output string you need at each step P numbers [0...R-1] (which can then serve as index into the replacement character list). Well, this is the definition of an integer with P digits in base R.
So let's write a helper class representing such integers:
class NDigitNumber
{
int[] _digits;
int _base;
// construct an integer with the specified numer of digits in the specified base
public NDigitNumber(int digits, int #base)
{
_digits = new int[digits];
_base = #base;
}
// get the digit at the specified position
public int this[int index] => _digits[index];
// increment the number, returns false on overflow
public bool Increment()
{
for (var pos = 0; pos < _digits.Length; pos++)
{
if (++_digits[pos] < _base)
break;
if (pos == _digits.Length-1)
return false;
for (var i = 0; i <= pos; i++)
_digits[i] = 0;
}
return true;
}
}
The Increment methods works like these mechanical counter devices where each digit wheel, when rotated from its maximum digit to the next, resets itself and all lower wheels to 0 and increments the next higher wheel.
Then we only have to iterate over all possible such integers to get the desired output:
var input = "a.b.";
var placeholder = '.';
var replacements = new[] { '1', '2', '3' };
// determine positions of placeholder in string
var placeholderPositions = new List<int>();
for (var i = 0; i < input.Length; i++)
{
if (input[i] == placeholder)
placeholderPositions.Add(i);
}
// iterate over all possible integers with
// placeholderPositions.Count digits
// in base replacements.Length
var number = new NDigitNumber(placeholderPositions.Count, replacements.Length);
do
{
var result = new StringBuilder(input);
for (var i = 0; i < placeholderPositions.Count; i++)
result[placeholderPositions[i]] = replacements[number[i]];
Console.WriteLine(result.ToString());
} while(number.Increment());
Output:
a1b1
a2b1
a3b1
a1b2
a2b2
a3b2
a1b3
a2b3
a3b3

Based on accepted answer of this post:
public static IEnumerable<string> Combinations(string template, string str, char placeholder)
{
int firstPlaceHolder = template.IndexOf(placeholder);
if (firstPlaceHolder == -1)
return new string[] { template };
string prefix = template.Substring(0, firstPlaceHolder);
string suffix = template.Substring(firstPlaceHolder + 1);
var recursiveCombinations = Combinations(suffix, str, placeholder);
return
from chr in str
from recSuffix in recursiveCombinations
select prefix + chr + recSuffix;
}
Usage:
List<string> combinations = Combinations("a.b.", "123", '.').ToList();

Reassigning a value to a character array not working

I am currently having issues reassigning a value to a character array. Below is my code (unfinished solution to find the next smallest palindrome):
public int nextSmallestPalindrome(int number)
{
string numberString = number.ToString();
// Case 1: Palindrome is all 9s
for (int i = 0; i < numberString.Length; i++)
{
if (numberString[i] != '9')
{
break;
}
int result = number + 2;
return result;
}
// Case 2: Is a palindrome
int high = numberString.Length - 1;
int low = 0;
bool isPalindrome = true;
for (low = 0; low <= high; low++, high--)
{
if (numberString[low] != numberString[high])
{
isPalindrome = false;
break;
}
}
char[] array = numberString.ToCharArray();
if (isPalindrome == true)
{
// While the middle character is 9
while (numberString[high] == '9' || numberString[low] == '9')
{
array[high] = '0';
array[low] = '0';
high++;
low--;
}
int replacedvalue1 = (int)Char.GetNumericValue(numberString[high]) + 1;
int replacedvalue2 = (int)Char.GetNumericValue(numberString[low]) + 1;
StringBuilder result = new StringBuilder(new string(array));
if (high == low)
{
result[high] = (char)replacedvalue1;
}
else
{
Console.WriteLine(result.ToString());
result[high] = (char)replacedvalue1;
Console.WriteLine(result.ToString());
result[low] = (char)replacedvalue2;
}
return Int32.Parse(result.ToString());
}
else return -1;
}
Main class runs:
Console.WriteLine(nextSmallestPalindrome(1001));
This returns 1001, then 101 and then gives a formatexception at the return Int32.Parse(result.ToString()); statement.
I am very confused, as I believe "result" should be 1101 after I assign result[high] = (char)replacedvalue1;. Printing replacedvalue1 gives me "1" as expected. However, debugging it line by line shows that "1001" turns into "1 1" at the end, signifying strange characters.
What could be going wrong?
Thanks

Characters and numbers aren't the same thing. I find it easiest to keep an ASCII chart open when doing this sort of thing.
If you look at one of those charts, you'll see that the character 0 actually has a decimal value of 48.
char c = (char)48; // Equals the character '0'
The reverse is also true:
char c = '0';
int i = (int)c; // Equals the number 48
You managed to keep chars and ints separate for the most part, but at the end you got them mixed up:
// Char.GetNumericValue('0') will return the number 0
// so now replacedvalue1 will equal 1
int replacedvalue1 = (int)Char.GetNumericValue(numberString[high]) + 1;
// You are casting the number 1 to a character, which according to the
// ASCII chart is the (unprintable) character SOH (start of heading)
result[high] = (char)replacedvalue1;
FYI you don't actually need to cast a char back-and-forth in order to perform operations on it. char c = 'a'; c++; is valid, and will equal the next character on the table ('b'). Similarly you can increment numeric characters:
char c = '0'; c++; // c now equals '1'
Edit: The easiest way to turn an integer 1 into the character '1' is to "add" the integer to the character '0':
result[high] = (char)('0' + replacedvalue1);
Of course there are much easier ways to accomplish what you are trying to do, but these techniques (converting and adding chars and ints) are good tools to know.

You do not have write that much code to do it.
Here is your IsPalindrome method;
private static bool IsPalindrome(int n)
{
string ns = n.ToString(CultureInfo.InvariantCulture);
var reversed = string.Join("", ns.Reverse());
return (ns == reversed);
}
private static int FindTheNextSmallestPalindrome(int x)
{
for (int i = x; i < 2147483647; i++)
{
if (IsPalindrome(i))
{
return i;
}
}
throw new Exception("Number must be less than 2147483647");
}
This is how you call it. You do not need an array to call it. You can just enter any number which is less than 2147483647(max value of int) and get the next palindrome value.
var mynumbers = new[] {10, 101, 120, 110, 1001};
foreach (var mynumber in mynumbers)
{
Console.WriteLine(FindTheNextPalindrome(mynumber));
}

String Combinations With Character Replacement

I am trying to work through a scenario I haven't seen before and am struggling to come up with an algorithm to implement this properly. Part of my problem is a hazy recollection of the proper terminology. I believe what I am needing is a variation of the standard "combination" problem, but I could well be off there.
The Scenario
Given an example string "100" (let's call it x), produce all combinations of x that swap out one of those 0 (zero) characters for a o (lower-case o). So, for the simple example of "100", I would expect this output:
"100"
"10o"
"1o0"
"1oo"
This would need to support varying length strings with varying numbers of 0 characters, but assume there would never be more than 5 instances of 0.
I have this very simple algorithm that works for my sample of "100" but falls apart for anything longer/more complicated:
public IEnumerable<string> Combinations(string input)
{
char[] buffer = new char[input.Length];
for(int i = 0; i != buffer.Length; ++i)
{
buffer[i] = input[i];
}
//return the original input
yield return new string(buffer);
//look for 0's and replace them
for(int i = 0; i != buffer.Length; ++i)
{
if (input[i] == '0')
{
buffer[i] = 'o';
yield return new string(buffer);
buffer[i] = '0';
}
}
//handle the replace-all scenario
yield return input.Replace("0", "o");
}
I have a nagging feeling that recursion could be my friend here, but I am struggling to figure out how to incorporate the conditional logic I need here.

Your guess was correct; recursion is your friend for this challenge. Here is a simple solution:
public static IEnumerable<string> Combinations(string input)
{
int firstZero = input.IndexOf('0'); // Get index of first '0'
if (firstZero == -1) // Base case: no further combinations
return new string[] { input };
string prefix = input.Substring(0, firstZero); // Substring preceding '0'
string suffix = input.Substring(firstZero + 1); // Substring succeeding '0'
// e.g. Suppose input was "fr0d00"
// Prefix is "fr"; suffix is "d00"
// Recursion: Generate all combinations of suffix
// e.g. "d00", "d0o", "do0", "doo"
var recursiveCombinations = Combinations(suffix);
// Return sequence in which each string is a concatenation of the
// prefix, either '0' or 'o', and one of the recursively-found suffixes
return
from chr in "0o" // char sequence equivalent to: new [] { '0', 'o' }
from recSuffix in recursiveCombinations
select prefix + chr + recSuffix;
}

This works for me:
public IEnumerable<string> Combinations(string input)
{
var head = input[0] == '0' //Do I have a `0`?
? new [] { "0", "o" } //If so output both `"0"` & `"o"`
: new [] { input[0].ToString() }; //Otherwise output the current character
var tails = input.Length > 1 //Is there any more string?
? Combinations(input.Substring(1)) //Yes, recursively compute
: new[] { "" }; //Otherwise, output empty string
//Now, join it up and return
return
from h in head
from t in tails
select h + t;
}

You don't need recursion here, you can enumerate your patterns and treat them as binary numbers. For example, if you have three zeros in your string, you get:
0 000 ....0..0....0...
1 001 ....0..0....o...
2 010 ....0..o....0...
3 011 ....0..o....o...
4 100 ....o..0....0...
5 101 ....o..0....o...
6 110 ....o..o....0...
7 111 ....o..o....o...
You can implement that with bitwise operators or by treating the chars that you want to replace like an odometer.
Below is an implementation in C. I'm not familiar with C# and from the other answers I see that C# already has suitable standard classes to implement what you want. (Although I'm surprised that so many peolpe propose recursion here.)
So this is more an explanation or illustration of my comment to the question than an implementation advice for your problem.
int binrep(char str[])
{
int zero[40]; // indices of zeros
int nzero = 0; // number of zeros in string
int ncombo = 1; // number of result strings
int i, j;
for (i = 0; str[i]; i++) {
if (str[i] == '0') {
zero[nzero++] = i;
ncombo <<= 1;
}
}
for (i = 0; i < ncombo; i++) {
for (j = 0; j < nzero; j++) {
str[zero[j]] = ((i >> j) & 1) ? 'o' : '0';
}
printf("%s\n", str); // should yield here
}
return ncombo;
}

Here's a solution using recursion, and your buffer array:
private static void Main(string[] args)
{
var a = Combinations("100");
var b = Combinations("10000");
}
public static IEnumerable<string> Combinations(string input)
{
var combinations = new List<string>();
combinations.Add(input);
for (int i = 0; i < input.Length; i++)
{
char[] buffer= input.ToArray();
if (buffer[i] == '0')
{
buffer[i] = 'o';
combinations.Add(new string(buffer));
combinations = combinations.Concat(Combinations(new string(buffer))).ToList();
}
}
return combinations.Distinct();
}
The method adds the raw input as the first result. After that, we replace in a loop the 0s we see as a o and call our method back with that new input, which will cover the case of multiple 0s.
Finally, we end up with a couple duplicates, so we use Distinct.

I know that the earlier answers are better. But I don't want my code to go to waste. :)
My approach for this combinatorics problem would be to take advantage of how binary numbers work. My algorithm would be as follows:
List<string> ZeroCombiner(string str)
{
// Get number of zeros.
var n = str.Count(c => c == '0');
var limit = (int)Math.Pow(2, n);
// Create strings of '0' and 'o' based on binary numbers from 0 to 2^n.
var binaryStrings = new List<string>();
for (int i = 0; i < limit; ++i )
{
binaryStrings.Add(Binary(i, n + 1));
}
// Replace each zero with respect to each binary string.
var result = new List<string>();
foreach (var binaryString in binaryStrings)
{
var zeroCounter = 0;
var combinedString = string.Empty;
for (int i = 0; i < str.Length; ++i )
{
if (str[i] == '0')
{
combinedString += binaryString[zeroCounter];
++zeroCounter;
}
else
combinedString += str[i];
}
result.Add(combinedString);
}
return result;
}
string Binary(int i, int n)
{
string result = string.Empty;
while (n != 0)
{
result = result + (i % 2 == 0 ? '0' : 'o');
i = i / 2;
--n;
}
return result;
}

Masking all characters of a string except for the last n characters

I want to know how can I replace a character of a string with condition of "except last number characters"?
Example:
string = "4111111111111111";
And I want to make it that
new_string = "XXXXXXXXXXXXX1111"
In this example I replace the character to "X" except the last 4 characters.
How can I possibly achieve this?

Would that suit you?
var input = "4111111111111111";
var length = input.Length;
var result = new String('X', length - 4) + input.Substring(length - 4);
Console.WriteLine(result);
// Ouput: XXXXXXXXXXXX1111

How about something like...
new_string = new String('X', YourString.Length - 4)
+ YourString.Substring(YourString.Length - 4);
create a new string based on the length of the current string -4 and just have it all "X"s. Then add on the last 4 characters of the original string

Here's a way to think through it. Call the last number characters to leave n:
How many characters will be replaced by X? The length of the string minus n.
How can we replace characters with other characters? You can't directly modify a string, but you can build a new one.
How to get the last n characters from the original string? There's a couple ways to do this, but the simplest is probably Substring, which allows us to grab part of a string by specifying the starting point and optionally the ending point.
So it would look something like this (where n is the number of characters to leave from the original, and str is the original string - string can't be the name of your variable because it's a reserved keyword):
// 2. Start with a blank string
var new_string = "";
// 1. Replace first Length - n characters with X
for (var i = 0; i < str.Length - n; i++)
new_string += "X";
// 3. Add in the last n characters from original string.
new_string += str.Substring(str.Length - n);

This might be a little Overkill for your ask. But here is a quick extension method that does this.
it defaults to using x as the masking Char but can be changed with an optional char
public static class Masking
{
public static string MaskAllButLast(this string input, int charsToDisplay, char maskingChar = 'x')
{
int charsToMask = input.Length - charsToDisplay;
return charsToMask > 0 ? $"{new string(maskingChar, charsToMask)}{input.Substring(charsToMask)}" : input;
}
}
Here a unit tests to prove it works
using Xunit;
namespace Tests
{
public class MaskingTest
{
[Theory]
[InlineData("ThisIsATest", 4, 'x', "xxxxxxxTest")]
[InlineData("Test", 4, null, "Test")]
[InlineData("ThisIsATest", 4, '*', "*******Test")]
[InlineData("Test", 16, 'x', "Test")]
[InlineData("Test", 0, 'y', "yyyy")]
public void Testing_Masking(string input, int charToDisplay, char maskingChar, string expected)
{
//Act
string actual = input.MaskAllButLast(charToDisplay, maskingChar);
//Assert
Assert.Equal(expected, actual);
}
}
}

StringBuilder sb = new StringBuilder();
Char[] stringChar = string.toCharArray();
for(int x = 0; x < stringChar.length-4; x++){
sb.append(stringChar[x]);
}
sb.append(string.substring(string.length()-4));
string = sb.toString();

I guess you could use Select with index
string input = "4111111111111111";
string new_string = new string(input.Select((c, i) => i < input.Length - 4 ? 'X' : c).ToArray());

Some of the other concise answers here did not account for strings less than n characters. Here's my take:
var length = input.Length;
input = length > 4 ? new String('*', length - 4) + input.Substring(length - 4) : input;

lui,
Please Try this one...
string dispString = DisplayString("4111111111111111", 4);
Create One function with pass original string and no of digit.
public string DisplayString(string strOriginal,int lastDigit)
{
string strResult = new String('X', strOriginal.Length - lastDigit) + strOriginal.Substring(strOriginal.Length - lastDigit);
return strResult;
}
May be help you....

Try this:
String maskedString = "...."+ (testString.substring(testString.length() - 4, testString.length()));

Late to the party but I also wanted to mask all but the last 'x' characters, but only mask numbers or letters so that any - ( ), other formatting, etc would still be shown. Here's my quick extension method that does this - hopefully it helps someone. I started with the example from Luke Hammer, then changed the guts to fit my needs.
public static string MaskOnlyChars(this string input, int charsToDisplay, char maskingChar = 'x')
{
StringBuilder sbOutput = new StringBuilder();
int intMaskCount = input.Length - charsToDisplay;
if (intMaskCount > 0) //only mask if string is longer than requested unmasked chars
{
for (var intloop = 0; intloop < input.Length; intloop++)
{
char charCurr = Char.Parse(input.Substring(intloop, 1));
byte[] charByte = Encoding.ASCII.GetBytes(charCurr.ToString());
int intCurrAscii = charByte[0];
if (intloop <= (intMaskCount - 1))
{
switch (intCurrAscii)
{
case int n when (n >= 48 && n <= 57):
//0-9
sbOutput.Append(maskingChar);
break;
case int n when (n >= 65 && n <= 90):
//A-Z
sbOutput.Append(maskingChar);
break;
case int n when (n >= 97 && n <= 122):
//a-z
sbOutput.Append(maskingChar);
break;
default:
//Leave other characters unmasked
sbOutput.Append(charCurr);
break;
}
}
else
{
//Characters at end to remain unmasked
sbOutput.Append(charCurr);
}
}
}
else
{
//if not enough characters to mask, show unaltered input
return input;
}
return sbOutput.ToString();
}

Programmatically check if a number is a palindrome

This sounds like homework, yes it is (of someone else), I asked a friend of mine who is learning C# to lend me some of his class exercises to get the hang of it.
So as the title says: How can I check if a number is a Palindrome?
I'm not asking for source code (although its very useful), but rather that someone explained how should the code should work, so that it can be applied to many different languages.
The Solution:
#statikfx searched SO for this and found the solution.
n = num;
while (num > 0)
{
dig = num % 10;
rev = rev * 10 + dig;
num = num / 10;
}
// If (n == rev) then num is a palindrome

I check for palindromes by converting the integer to a string, then reversing the string, then comparing equality. This will be the best approach for you since you're just starting out.
Since you're working in C# and this is homework, I'll use very obscure-looking Python that won't help you:
def is_palindrome(i):
s = str(i)
return s[::-1] == s
Convert that to C# and you'll have your answer.

Main idea:
Input number: 12321
Splitting the digits of the number, put them into an array
=> array [1, 2, 3, 2, 1]
Check if array[x] = array[arr_length - x] for all x = 0..arr_length / 2
If check passed => palindrome

There are many ways. Probably the simplest is to have 2 indexes, i at beginning and j at end of number. You check to see if a[i] == a[j]. If so, increment i and decrement j. You stop when i > j. When looping if you ever reach a point where a[i] != a[j], then it's not a palindrome.

Here's some working code. The first function tests if a number is palidromic by converting it to a string then an IEnumerable and testing if it is equal to its reverse. This is enough to answer your question. The main function simply iterates over the integers testing them one by one.
using System;
using System.Collections.Generic;
using System.Linq;
class Program
{
public static bool IsPalindromic(long l)
{
IEnumerable<char> forwards = l.ToString().ToCharArray();
return forwards.SequenceEqual(forwards.Reverse());
}
public static void Main()
{
long n = 0;
while (true)
{
if (IsPalindromic(n))
Console.WriteLine("" + n);
n++;
}
}
}
Update: Here is a more direct method of generating palindromes. It doesn't test numbers individually, it just generates palindromes directly. It's not really useful for answering your homework, but perhaps you will find this interesting anyway:
using System;
using System.Collections.Generic;
using System.Linq;
class Program
{
public static void Main()
{
bool oddLength = true;
ulong start = 1;
while (true)
{
for (ulong i = start; i < start * 10; ++i)
{
string forwards = i.ToString();
string reverse = new string(forwards.ToCharArray()
.Reverse()
.Skip(oddLength ? 1 : 0)
.ToArray());
Console.WriteLine(forwards + reverse);
}
oddLength = !oddLength;
if (oddLength)
start *= 10;
}
}
}

My solution:
bool IsPalindrome(string str)
{
if(str.Length == 1 || str.Length == 0) return true;
return str[0] == str[str.Length-1] && IsPalindrome(str.Substring(1,str.Length-2));
}

Here's some pseudocode:
function isPalindrome(number) returns boolean
index = 0
while number != 0
array[index] = number mod 10
number = number div 10
index = index + 1
startIndex = 0;
endIndex = index - 1
while startIndex > endIndex
if array[endIndex] != array[startIndex]
return false
endIndex = endIndex - 1
startIndex = startIndex + 1
return true
Note that that's for base 10. Change the two 10s in the first while loop for other bases.

The following function will work for both numbers as well as for strings.
public bool IsPalindrome(string stringToCheck)
{
char[] rev = stringToCheck.Reverse().ToArray();
return (stringToCheck.Equals(new string(rev), StringComparison.OrdinalIgnoreCase));
}
zamirsblog.blogspot.com

in theory you want to convert the number to a string. then convet the string to an array of characters and loop the array comparing character (i) with character (array length - i) if the two characters are not equal exit the loop and return false. if it makes it all the way through the loop it is a Palindrome.

Interesting. I'd probably convert the number to a string, and then write a recursive function to decide whether any given string is a palendrome.

int n = check_textbox.Text.Length;
int check = Convert.ToInt32(check_textbox.Text);
int m = 0;
double latest=0;
for (int i = n - 1; i>-1; i--)
{
double exp = Math.Pow(10, i);
double rem = check / exp;
string rem_s = rem.ToString().Substring(0, 1);
int ret_rem = Convert.ToInt32(rem_s);
double exp2 = Math.Pow(10, m);
double new_num = ret_rem * exp2;
m=m+1;
latest = latest + new_num;
double my_value = ret_rem * exp;
int myvalue_int = Convert.ToInt32(my_value);
check = check - myvalue_int;
}
int latest_int=Convert.ToInt32(latest);
if (latest_int == Convert.ToInt32(check_textbox.Text))
{
MessageBox.Show("The number is a Palindrome number","SUCCESS",MessageBoxButtons.OK,MessageBoxIcon.Information);
}
else
{
MessageBox.Show("The number is not a Palindrome number","FAILED",MessageBoxButtons.OK,MessageBoxIcon.Exclamation);
}

public class Main {
public static boolean Ispalindromic(String word) {
if (word.length() < 2) {
return true;
}
else if (word.charAt(0) != word.charAt(word.length() - 1)) {
return false;
} else {
Ispalindromic(word.substring(1, word.length() - 1));
}
return true;
}
public static void main(String args[]) {
Scanner sc = new Scanner(System.in);
String word = sc.nextLine();
System.out.println(Ispalindromic(word) ? "it is palidromic" : "it is not palidromic");
}
}

This is my solution coming from a beginner:
Console.Write("Enter a number to check if palindrome: ");
bool palindrome = true;
int x = int.Parse(Console.ReadLine());
/* c is x length minus 1 because when counting the strings
length it starts from 1 when it should start from 0*/
int c = x.ToString().Length - 1;
string b = x.ToString();
for (int i = 0; i < c; i++)
if (b[i] != b[c - i])
palindrome = false;
if (palindrome == true)
Console.Write("Yes");
else Console.Write("No");
Console.ReadKey();

You need to reverse the number then compare the result to the original number.
If it matches, you have a palindrome. It should work irrespective of the number being even, odd or symmetric.
public static bool IsNumberAPalindrome(long num)
{
return long.Parse(string.Join("", num.ToString().ToCharArray().Reverse().ToArray())) == num ? true : false;
}

The implementation is bellow:
public bool IsPalindrome(int x) {
string test = string.Empty;
string res = string.Empty;
test = x.ToString();
var reverse = test.Reverse();
foreach (var c in reverse)
{
res += c.ToString();
}
return test == res;
}

You have a string, it can have integers, it can have characters, does not matter.
You convert this string to an array, depending on what types of characters the strings consist of, this may use to toCharArray method or any other related method.
You then use the reverse method that .NET provides to reverse your array, now you have two arrays, the original one and the one you reversed.
You then use the comparison operator (NOT THE ASSIGNMENT OPERATOR!) to check if the reversed one is the same as the original.

something like this
bool IsPalindrome(int num)
{
var str = num.ToString();
var length = str.Length;
for (int i = 0, j = length - 1; length/2 > i; i++, j-- ){
if (str[i] != str[j])
return false;
}
return true;
}
you could even optimise it