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C#--Counting the number of occurrences of a single digit(int) in a string--not working with int to char converted Variable

I'm trying to count the number of times an int appears in a string
int count = numbers
.Where(x => x == '0')
.Count();
If I type in the literal number I want to check for as seen above '0' it works.
But I want to use this as a method where I can check for other digits. This, unfortunately, doesn't work when I convert an int to a char and insert the digit variable
char digit = Convert.ToChar(0);
int count= numbers
.Where(x => x == digit)
.Count();
What am I doing wrong?

Convert.ToChar(Int32) returns Unicode character equivalent to the value of passed int. For example it will convert 65 to A:
Console.WriteLine(Convert.ToChar(65)); // prints "A"
If I understand your requirement correctly you can call ToString and take first char of resulting string instead of Convert.ToChar(0):
char digit = 0.ToString()[0]
Or as this answer suggests:
char c = (char)(i + 48);

Convert.ToChar(0) converts you bit representation to the according to the character encoding table (e.g. ASCII) . 0 in this case is a Null character. Whereas bit representation of a '0' character is 48 according to the table
You can use this snippet to compare you int digit to the chars
string numbers = "33";
int digit = 3;
int count = numbers
// '0' -'0' (48 - 48) will give you 0 int value,
// '1' - '0' (49 - 48) will give you 1 etc.
.Where(x => x - '0' == digit)
.Count();
but keep in mind that you digit might be greater than 9, then it would take more than one character and this is going a bit different problem.

Display the sum of digits in a number entered by the user

I need to get a number from the user and display the sum of that number's digits. For example, the sum of the digits in the number 12329 is 17.
Here's what I tried to do and it is giving me the ASCII code instead:
Console.WriteLine("please enter a number: ");
string num = Console.ReadLine();
int len = num.Length;
int[] nums = new int[len];
int sum = 0;
int count = 0;
while (count < len)
{
nums[count] = Convert.ToInt32(num[count]);
count++;
}
for (int i = 0; i < len; i++)
sum += nums[i];
Console.WriteLine(sum);

This is a very common mistake. char is really just a number - the encoding value of the character represented by the char. When you do Convert.ToInt32 on it, it sees the char as a number and says "alright let's just convert this number to 32 bits and return!" instead of trying to parse the character.
"Wait, where have I used a char in my code?" you might ask. Well, here:
Convert.ToInt32(num[count]) // 'num[count]' evaluates to 'char'
To fix this, you need to convert the char to a string:
nums[count] = Convert.ToInt32(num[count].ToString());
^^^^^^^^^^^^^^^^^^^^^
Now you are calling a different overload of the ToInt32 method, which actually tries to parse the string.

When you access your string with a index (in your case num[count]) you get a char type and because of that you are getting ASCII values. You can convert char to string with .ToString() in your case nums[count] = Convert.ToInt32(num[count].ToString());.I posted here another approach to your problem:
string number = Console.ReadLine();
int sum = 0;
foreach (var item in number)
{
sum += Convert.ToInt32(item.ToString());
}
Console.WriteLine(sum);

As you noticed the Convert.ToInt32(num[count]) will only return the Unicode code of the char you want to convert, because when you use the [] operator on a string, you will get readonly access to [the] individual characters of a string [1].
And so you are using Convert.ToInt32(Char), which
Converts the value of the specified Unicode character to the equivalent 32-bit signed integer.
One way to cast the numeric value from a char to a digit, is using Char.GetNumericValue(), which
Converts a specified numeric Unicode character to a double-precision floating-point number.
By using System.Linq; you can cut your code to just a few lines of code.
Console.WriteLine("please enter a number: ");
string num = Console.ReadLine(); // "12329"
int sum = (int)num.Select(n => Char.GetNumericValue(n)).Sum();
Console.WriteLine(sum); // 17
What does this line of code?
The num.Select(n => Char.GetNumericValue(n)) will iterate over each char in your string, like your while and converts each value to a double value and return an IEnumerable<double>. The Sum() itself will iterate over each value of the IEnumerable<double> and calculate the sum as a double. And since you want an integer as result the (int) casts the double into an integer value.
Side-Note:
You could check your input, if it is really an integer.
For example:
int intValue;
if(Int32.TryParse(num, out intValue))
{
// run the linq
}
else
{
// re-prompt, exit, ...
}
If you are using Char.GetNumericValue() on an letter it will return -1 so for example the sum of string num = "123a29"; will be 16.

Convert chars corresponding to digits to uint

I need to travers the string ,which should be the string of digits and make some arithmetic operations on these digits
for (int i = data.Length - 1; i >= 0; --i)
{
uint curDigit;
//Convert to uint the current rightmost digit, if convert fails return false (the valid data should be numeric)
try
{
curDigit = Convert.ToUInt32(data[i]);
//arithmetic ops...
}
catch
{
return false;
}
I test it with the following input data string.
"4000080706200002"
For i = 15,corresponding to the rightmost digit 2,I get 50 as an output from
curDigit = Convert.ToUInt32(data[i]);
Can someone please explain me what is wrong?and how to correct the issue

50 is the ascii code for '2'. what you need is '2' - '0' (50-48)
byte[] digits = "4000080706200002".Select(x => (byte)(x - '0')).ToArray();
http://www.asciitable.com/

What you are getting back is the ascii value of character 2, You can use call ToString on the character item and then call Convert.ToUnit32, Consider the example:
char x = '2';
uint curDigit = Convert.ToUInt32(x.ToString());
this will give you back 2 as curDigit
For your code you can just use:
curDigit = Convert.ToUInt32(data[i].ToString());
Another option is to use char.GetNumericValue like:
uint curDigit = (UInt32) char.GetNumericValue(data[i]);
char.GetNumericValue returns double and you can cast the result back to UInt32

The problem is that data[i] returns a char variable, that essentialy is an integer holding the ASCII code of the character. So '2' corresponds to 50.
There are 2 things you can do to overcome this behaviour:
Better curDigit = Convert.ToUInt32(data[i] - '0'); //Substract the ASCII representation of '0' from the char
curDigit = Convert.ToUInt32(data.Substring(i,1)); //Use substring to return a string instead of char. Note, that this method is less efficient, as Convert from string essentially splits the string into chars, and substract '0' from each and every one of them.

Your getting the ASCII (or Unicode) values for those characters. The problem is that the code points for the characters '0' … '9' are not 0 … 9, but 48 … 57. To fix this, you need to adjust by that offset. For example:
curDigit = Convert.ToUInt32(data[i] - '0');
Or
curDigit = Convert.ToUInt32(data[i] - 48);

Rather than messing around with ASCII calculations you could use UInt32.TryParse as an alternative solution. However, this method requires a string input not char, so you would have to modify your approach a little:
string input = "4000080706200002";
string[] digits = input.Select(x => x.ToString()).ToArray();
foreach(string digit in digits)
{
uint curDigit = 0;
if(UInt32.TryParse(digit, out curDigit))
{
//arithmetic ops...
}
//else failed to parse
}

Get ASCII from int variable

Here is what I've tried
int two = 2;
int asciiX = (int) 'x';
int asciiTwo = (int) two;
Console.WriteLine("The ascii value of 2 is " + asciiTwo);
Console.WriteLine("The ascii value of x is " + asciiX););
I expected the output to be 50 as the ascii value of 2 is 50 (which is the ASCII code of '2')
But I got this result :
The ascii value of 2 is 2
The ascii value of x is 120 (it's working for x)
I know that if I put int asciiTwo = '2'; it will works, but it's not directly processing from the variable how can I do, to get the ascii code of a number which is in a int variable ?

two is an int with value 2. You are casting an int to an int. That does not change anything.
You can get the ASCII value using two ways at least:
(int)(two.ToString())[0] //the first char of the string representation of two
(int)(two + '0') //numbers start at '0' in the ASCII table

You declare the two variable as int. The int of an int is the int itself.
What you want is to declare it as char or string, too.
char two = '2';
int asciiTwo = (int) two;

How to convert an integer to fixed length hex string in C#?

I have an integer variable with max value of 9999.
I can convert to fixed length string (4-characters):
value.ToString("0000");
and I can convert it to hex:
value.ToString("X");
I want to convert it to a hex string of four characters (padded with 0 at the left if the value is converted to less than four digits hex value). I tried the following which didn't work.
value.ToString("0000:X");
OK, I can check the length of hex string and pad left with zeros.
But is there any straightforward way?

Use a number after the X format specifier to specify the left padding : value.ToString("X4")

String.Format( "{0:X2}", intValue)

Here is another method,
You can define a function and pass it 2 values, one the actual number and the second is the max length to fix.
i.e.
public string FixZero(string str, int maxlength)
{
string zero = "000000000000000000000000000000000000000";
int length = str.Length;
int diff = maxlength- length;
string z = zero.Substring(1, diff);
z = z + str;
return z;
}
you need integers in the format 0012, FixZero("12", 4)
or for 0001234, FixZero("1234", 7)