title: missing prototype error
body: <p>I'm getting an error I don't understand and can't find a solution.</p>
  
  <p>The error is as follows:</p>
  
  <p>missing prototype for isANumber</p>
  
  <p>the code it refers to is:</p>
  
  <pre><code>double prompt(char *promptString) {
  
      printf("%s", promptString);
      char *input = "";
      scanf("%s", &amp;*input);
      printf("%s\n", &amp;*input);
  
      int check = isANumber(input);
  
  
  if (check) {
      return (double) *input;
  } else {
      return 0.00;
  }
  
  }
  
  int isANumber(char *check) {
  
      int result = 0;    /* Current isdigit() return value */
      do                           /* Check that each character of the...*/
          result = isdigit(*check++);  /* ...string is a digit and move on...*/
      while (result &amp;&amp; *check);       /* ...until non-digit found or at EOS */
      return result;  /* Return result of last isdigit() call */
  
  }
  </code></pre>
  
  <p>libraries included:</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include &lt;limits.h&gt;
  #include &lt;ctype.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;string.h&gt;
  </code></pre>
  
  <p>Any help would be appreciated :)</p>