user19411: I have a byte variable CardNumberByte with a value of E8 if i print out as HEX:
Serial.println(CardNumberByte, HEX)

which returns E8.
What I would like to do is to "append 0x as prefix" so that it is equivalent to 
Char CardNumberByte=0xE8;

how should i concatenate 0x to CardNumberByte?
here is the reason i need to do so.
Thanks

user10394: I've looked at you question and the question you linked two and I've tried to join the dots to give you an answer, so I might be well off the mark, but...
I think you might have misunderstood what 0x28 means.
0x?? means that the ?? represent a hexadecimal number rather than a decimal number.
So 10 (Ten) in decimal is the same as 0x0A in hex or B00001010 or in binary or even 012 in octal.  (See https://www.arduino.cc/en/Reference/IntegerConstants for more details)
So you want to have some code that says:
char Address = 0x28;

This is assigning the hexadecimal value 28 to the variable Address.  You could also write:
char Address = 40;

In this case you are assigning the value decimal 40 (which is hex 28) to the variable.  If you want to write strange code that is misleading you could write:
char Address = '(';  // ( is ASCII character 0x28 or 40 - Don't do it like this!

One other important thing here is that the char type in this case is not being used as type that holds a printable character, its being used as a signed 8 bit number.  

19411: <p>I have a <strong>byte</strong> variable CardNumberByte with a value of E8 if i print out as HEX:</p>

<pre><code>Serial.println(CardNumberByte, HEX)
</code></pre>

<p>which returns E8.</p>

<p>What I would like to do is to "append 0x as prefix" so that it is equivalent to </p>

<pre><code>Char CardNumberByte=0xE8;
</code></pre>

<p>how should i concatenate 0x to CardNumberByte?</p>

<p><a href="https://arduino.stackexchange.com/questions/39861/how-to-convert-an-hex-string-to-an-array-of-bytes">here</a> is the reason i need to do so.</p>

<p>Thanks</p>
 10394: <p>I've looked at you question and the question you linked two and I've tried to join the dots to give you an answer, so I might be well off the mark, but...</p>

<p>I think you might have misunderstood what <code>0x28</code> means.</p>

<p>0x?? means that the ?? represent a hexadecimal number rather than a decimal number.</p>

<p>So 10 (Ten) in decimal is the same as 0x0A in hex or B00001010 or in binary or even 012 in octal.  (See <a href="https://www.arduino.cc/en/Reference/IntegerConstants" rel="nofollow noreferrer">https://www.arduino.cc/en/Reference/IntegerConstants</a> for more details)</p>

<p>So you want to have some code that says:</p>

<pre><code>char Address = 0x28;
</code></pre>

<p>This is assigning the hexadecimal value 28 to the variable <code>Address</code>.  You could also write:</p>

<pre><code>char Address = 40;
</code></pre>

<p>In this case you are assigning the value decimal 40 (which is hex 28) to the variable.  If you want to write strange code that is misleading you could write:</p>

<pre><code>char Address = '(';  // ( is ASCII character 0x28 or 40 - Don't do it like this!
</code></pre>

<p>One other important thing here is that the <code>char</code> type in this case is not being used as type that holds a printable character, its being used as a signed 8 bit number.  </p>
