isalpha implementation C
<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>