title: isalpha implementation C
body: <p>just for fun I wrote this implementation of isalpha and it works but I have a lot of warnings, can you tell me how to fix them, or how can I do it in better way?</p>
  
  <p>Warnings:</p>
  
  <p>Line 6: comparision between pointer and integer</p>
  
  <p>Line 23: passing argument 1 of 'pointer' makes pointer from integer without a cast</p>
  
  <pre><code>#include &lt;stdlib.h&gt;
  #include &lt;stdio.h&gt;
  
  int my_isalpha(char *mark)
  {
      if((((mark)&gt;=0x41)&amp;&amp;((mark)&lt;=0x5A)||((mark)&gt;=0x61)&amp;&amp;((mark)&lt;=0x7A))) //WARNING
       return 1;
  
     else
      return 0;
  }
  
  
  int main()
  {
     char mark;
     int (*pointer)(char*);
     pointer=my_isalpha;
  
     printf("Your mark: ");
     scanf("%c",&amp;mark);
  
     if(pointer(mark))  //WARNING
       printf("TRUE");
  
     else
      printf("FALSE");
  
    return 0;
  }
  </code></pre>