While (* next! = NULL) loop not exiting when pointer is NULL

Please help me with this problem, the while loop in the following C code doesn't seem to end when * next == NULL and tries to call strlen (* next) with a bad ptr in Visual Studio 2010 Express.I tried everything I could come up with no result. The code tries to find the shortest and longest strings in an array of strings.

char *stringsInArray[] = {"green mats", "cat", "sat", "on", "the", "green mat", NULL};
char *shortest, *longest, **current, **next, **end;

current = stringsInArray;
next = stringsInArray + 1;
shortest = stringsInArray[0];
longest = stringsInArray[0];

while (*next != NULL) 
{
    if (strlen(*current) < strlen(*next))
    {
        if (strlen(shortest) > strlen(*next))
            shortest = *next;
        if (strlen(*current) < strlen(shortest))
       shortest = *current;
        if (strlen(*next) > strlen(longest))
            longest = *next;
    }  
    else
    if (strlen(*current) > strlen(*next))
    {
        if (strlen(*current) > strlen(longest))
      longest = *current;
        if (strlen(*next) < strlen(shortest))
      shortest = *next;
    }
    else // strlen(*stringsInArray) == strlen(*next)
    {
        // do nothing
    }

   *current++;
   *next++;
} 

printf("shortest string: %s\n",*shortest);
printf("longest string: %s\n",*longest);