title: What is the simplest way of using isdigit() and isalpha() commands?
body: <p>I need a brief explanation on how the two commands <code>isdigit()</code> and <code>isalpha()</code> work. Of course, I read online sources before asking the question, but I tried them and couldn't get them to work. What is the simplest way of using them? </p>
  
  <p>I know it gives back a value, so I'm assuming I can use it like this:</p>
  
  <pre><code>if(isdigit(someinput)==1)
   return -1;
  </code></pre>
  
  <p>Is that correct? Can I use this for any type of character? And can I compare it with a float number or array?</p>
  
  <p>Suppose, I want to scanf a text file that has numbers and letter and determine what I'm scanning. Can these two commands be used in this context?</p>