title: What is the difference between isdigit() and isnumber()?
body: <p>I have the function isnumber() in my ctype.h. I don’t find references of this function in the books I have neither in <a href="http://www.cplusplus.com/reference/cctype/" rel="nofollow">http://www.cplusplus.com/reference/cctype/</a> for consult. 
  I intend to detect and show the difference between isdigit() and isnumber() by a simple  example, but there is not (besides, U+0C6A, U+0ED2 and ½ are undetectable by the functions). 
  Is there any difference? How could I resolve that? </p>
  
  <pre><code>int main(int, char *[])
  {
      string text("Hello½123, Poly౪ ໒girl0.5!!!");
      decltype(text.size()) punct = 0, alpha = 0, number = 0, space = 0, digit = 0, graf = 0;
      for(auto i : text) {
          if(ispunct(i)){
              cout &lt;&lt; i &lt;&lt; "&lt;punct  ";
              ++punct;
          }
          if(isalpha(i)) {
              cout &lt;&lt; i &lt;&lt; "&lt;alpha  ";
              ++alpha;
          }
          if(isnumber(i)) {
              cout &lt;&lt; i &lt;&lt; "&lt;number  ";
              ++number;
          }
          if(isdigit(i)) {
              cout &lt;&lt; i &lt;&lt; "&lt;digit  ";
              ++digit;
          }
          if(isgraph(i)) {
              cout &lt;&lt; i &lt;&lt; "&lt;graph  ";
              ++graf;
          }
          if(isspace(i))
              ++space;
      }
      cout &lt;&lt; endl &lt;&lt; "There is " &lt;&lt; endl;
      cout &lt;&lt; punct &lt;&lt;  " puncts," &lt;&lt; endl;
      cout &lt;&lt; alpha &lt;&lt; " alphas," &lt;&lt; endl;
      cout &lt;&lt; number &lt;&lt; " numbers," &lt;&lt; endl;
      cout &lt;&lt; digit &lt;&lt; " digits," &lt;&lt; endl;
      cout &lt;&lt; graf &lt;&lt; " graphs," &lt;&lt; endl;
      cout &lt;&lt; space &lt;&lt; " spaces" &lt;&lt; endl;
      cout &lt;&lt; "in " &lt;&lt; text &lt;&lt; endl;
  
      return 0;
  }
  </code></pre>
  
  <p>A part of the result:</p>
  
  <pre><code>...
  
  5 numbers,
  5 digits,
  23 graphs,
  2 spaces
  in Hello½123, Poly౪ ໒girl0.5!!!
  </code></pre>