title: How exactly are data types represented in a computer?
body: <p>I'm a beginning programmer reading K&amp;R, and I feel as if the book assumes a lot of previous knowledge. One aspect that confuses me is the actual representation, or should I say existence, of variables in memory. What exactly does a data type specify for a variable? I'm not too sure of how to word this question... but I'll ask a few questions and perhaps someone can come up with a coherent answer for me.</p>
  
  <p>When using getchar(), I was told that it is better to use type "int" than type "char" due to the fact that "int" can hold more values while "char" can hold only 256 values. Since we may need the variable to hold the EOF value, we will need more than 256 or the EOF value will overlap with one of the 256 characters. In my mind, I view this as a bunch of boxes with empty holes. Could someone give me a better representation? Do these "boxes" have index numbers? When EOF overlaps with a value in the 256 available values, can we predict which value it will overlap with?</p>
  
  <p>Also, does this mean that the data type "char" is only fine to use when we are simply assigning a value to a variable manually, such as char c = 'a', when we definitely know that we will only have 256 possible ASCII characters?</p>
  
  <p>Also, what is the actual important difference between "char" and "int"? If we can use "int" type instead of "char" type, why do we decide to use one over the other at certain times? Is it to save "memory" (I use quotes as I do not actually how "memory" exactly works).</p>
  
  <p>Lastly, how exactly is the 256 available values of type char obtained? I read something about modulo 2^n, where n = 8, but why does that work (something to do with binary?). What is the modulo portion of "modulo 2^n" mean (if it has any relevance to modular arithmetic, I can't see the relation...)?</p>