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Converting int to hex but not string

Now I know that converting a int to hex is simple but I have an issue here.
I have an int that I want to convert it to hex and then add another hex to it.
The simple solution is int.Tostring("X") but after my int is turned to hex, it is also turned to string so I can't add anything to it until it is turned back to int again.
So my question is; is there a way to turn a int to hex and avoid having turned it to string as well. I mean a quick way such as int.Tostring("X") but without the int being turned to string.

I mean a quick way such as int.Tostring("X") but without the int being
turned to string.
No.
Look at this way. What is the difference between those?
var i = 10;
var i = 0xA;
As a value, they are exactly same. As a representation, first one is decimal notation and the second one is hexadecimal notation. The X you use hexadecimal format specifier which generates hexadecimal notation of that numeric value.
Be aware, you can parse this hexadecimal notation string to integer anytime you want.
C# convert integer to hex and back again

There is no need to convert. Number ten is ten, write it in binary or hex, yes their representation will differ depending in which base you write them but value is same. So just add another integer to your integer - and convert the final result to hex string when you need it.
Take example. Assume you have
int x = 10 + 10; // answer is 20 or 0x14 in Hex.
Now, if you added
int x = 0x0A + 0x0A; // x == 0x14
Result would still be 0x14. See?
Numeric 10 and 0x0A have same value just they are written in different base.
Hexadecimal string although is a different beast.
In above case that could be "0x14".
For computer this would be stored as: '0', 'x', '1', '4' - four separate characters (or bytes representing these characters in some encoding). While in case with integers, it is stored as single integer (encoded in binary form).

I guess you missing the point what is HEX and what is INT. They both represent an numbers. 1, 2, 3, 4, etc.. numbers. There's a way to look at numbers: as natural numbers: INT and hexadecimal - but at the end those are same numbers. For example if you have number: 5 + 5 = 10 (int) and A (as hex) but it the same number. Just view on them are different

Hex is just a way to represent number. The same statment is true for decimal number system and binary although with exception of some custom made numbers (BigNums etd) everything will be stored as binary as long as its integer (by integer i mean not floating point number). What would you really like to do is probably performing calculations on integers and then printing them as a Hex which have been already described in this topic C# convert integer to hex and back again

The short answer: no, and there is no need.
The integer One Hundred and seventy nine (179) is B3 in hex, 179 in base-10, 10110011 in base-2 and 20122 in base-3. The base of the number doesn't change the value of it. B3, 17, 10110011, and 20122 are all the same number, they are just represented different. So it doesn't matter what base they are in as long as you do you mathematical operations on numbers in the same base it doesn't matter what the base is.
So in your case with Hex numbers, they can contain characters such as 'A','B', 'C', and so on. So when you get a value in hex if it is a number that will contain a letter in its hex representation it will have to be a string as letters are not ints. To do what you want, it would be best to convert both numbers to regular ints and then do math and convert to Hex after. The reason for this is that if you want to be able to add (or whatever operation) with them looking like hex you are going to to need to change the behavior of the desired operator on string which is a hassle.

C# Save user input as binary

So I just learned how to convert ints to binary with Convert.ToString(int , 2);
Now I can use this so ask a user for a number and then save it with
int name = int.Parse(Console.ReadLine());
and then convert it with
Convert.ToString(name , 2);
to get the number in binary.
But I'm wondering if the user could input it in binary and then I could save it as is, to later convert the user input into decimal with
Convert.ToInt32(binary,2).ToString();
I know this isn't correct but just to give you an idea of what I'm looking for here is an example, instead of int you could use binary. Like
binary name = binary.Parse(Console.ReadLine());

You will read a string input from Console.ReadLine - but you can just use Convert.ToInt32(val, 2) to convert a base 2 string to a number.
If you really want to create a binary number type, you will need to define a struct with implicit or explicit conversion to an int, but this seems unneccessary for your task. But, they key point here is that an int is kind of base agnostic - it's the value represented by a string in base whatever.

I think you're slightly confused - when you "convert int's to binary" all you're actually doing is converting the int into a string in it's binary representation. It's not actually binary - it's just a string that contains 1's and 0's that represent a binary number.
To accomplish your goal, all you need to do is:
string binary = Console.ReadLine();
And the user would need to enter "binary" such as 0100. Again, I put binary in quotes because it's still just a string, not a number. If you want the user to enter a number, like 4 and store it as a string of 0100, just do:
string binary = Convert.ToString(int.Parse(Console.ReadLine()), 2);
which will read the user input (4), convert it to an integer, and then convert it to it's string binary representation (0100).
To read it back to an int, do Convert.ToInt32(binary, 2);

byte ToString without converting from hexidecimal

I am using c# to read information coming out of a scale and I am getting back 6 bytes of Data. The last two contain the weight, in Hexadecimal. The way that it is set up is that if your append byte 5 on to byte 4 and convert to decimal you will get the correct weight.
I am trying to do this right now by using toString on the bytes and appending them but toString is automatically converting them from Hexadecimal to decimal. This is occurring before I can append them so I am getting incorrect weights.
Is there any way to convert a byte to a string without it being formatted from hexadecimal to decimal for you?

Use the X format string when calling ToString on your bytes to keep them in hexadecimal. You can append a number to X to specify the number of "digits" you want.
byte b = 0x0A;
b.ToString("X"); // A
b.ToString("X2"); // 0A

File.WriteAllBytes does not changes file to binary 10101011

I have a some confusion about the function File.WriteAllBytes.
Actually i read from an image file using
byte[] b = System.IO.File.ReadAllBytes(textBox1.Text);
and then i wrote back the read data to a text file to see how it looks.
System.IO.File.WriteAllBytes(#"D:\abc.txt", b);
But the contents of abc.txt are not pure binary(1010110) , but they appear as :-
ëžÕwN±k›“ùIRA=Ï¥Dh﬒ȪÊj:³0Æî(À÷«3ÚÉid¤n•O<‰-ª#–¢)cùY³Ö˜K„TûËEÇóþ}wtÑ+²=£v*NÌ!\ äji;âíÇ8ÿ ?犴ö¬€Áç#µ:+ŠVÜ„©³Û?çù~VèÖ·ÂËSŠE7RH8}GJGfT?Ý?çüÿ œÌÊR"6­ÓŠY¬Š¬L§|n¹> ÷’ÃU{D®t­vE!3** Ý× õ¨ã(¨qžO§ùÿ >Ó¥¤…K€#N{ñM(ÊÅ€ûÃŒRtj/²Æ¤¶¹RÁŽxqþÏó#KŒîn皘æ0C/-Ž1Mu>oÊ }é5(­Q¢i±pIôÀôÿ ?çÒÂB-á.ãï©Ú}êB®æÇÌyÿ ?çüU¥mã$”ã
‚DiFQ¸'µ,ARGLäc¯4%ËŸÃœsŸóù~H 3d‚zŠ‡Ø........................................
Are the binary 1s and 0s getting converted to some other number system comprising of so many symbols ??

A text-viewer like NotePad will try to interpret the bytes as text, probably it will interpret the bytes as Unicode.
If you want to see the actual 0's and 1's then read in the image as bytes and convert the byte array to a string of 0's and 1's, for this you could use:
public static string ByteArrayToString(byte[] ba)
{
string hex = BitConverter.ToString(ba);
return hex.Replace("-","");
}
The conversion function is copied from here (accepted answer). Remember, this string will not anymore be interpretable as image, essentially this will simply be a large string of 0's and 1's.

Each byte in the file is comprised of 8 bits. When you use ReadAllBytes, you get an array of byte instances, where each byte represents a number between 0 and 255 (inclusive). One representation of the number 86 that is readable by humans is 01010110. However, when you use WriteAllBytes, it writes the sequence of bytes in the original form. Notepad is then loading the file and displaying each byte as a single character (or in some encodings treating multiple bytes as a single character to display). However, if you were to write "01010110" to a file such that Notepad shows those numbers, you would actually end up writing 8 bytes, not 8 bits, like this, where each set of 8 bits represents the digit '0' or '1':
00110000 00110001 00110000 00110001 00110000 00110001 00110001 00110000

Succinct way to write a mixture of chars and bytes?

I'm trying to write an index file that follows the format of a preexisting (and immutable) text file.
The file is fixed length, with 11 bytes of string (in ASCII) followed by 4 bytes of long for a total of 15 bytes per line.
Perhaps I'm being a bit dim, but is there an simple way to do this? I get the feeling I need to open up two streams to write one line - one for the string and one for the bytes - but that feels wrong.
Any hints?

You can use BitConverter to convert between an int/long and an array of bytes. This way you would be able to write eleven bytes followed by four bytes, followed by eleven more bytes, and so on.
byte[] intBytes = BitConverter.GetBytes(intValue); // returns 4-byte array
Converting to bytes: BitConverter.GetBytes(int).
Converting back to int: BitConverter.ToInt32(byte\[\], int)
If you are developing a cross-platform solution, keep in mind the following note from the documentation (thanks to uriDium for the comment):
The order of bytes in the array returned by the GetBytes method depends on whether the computer architecture is little-endian or big-endian.