Thread: problem with getting correct string length

I am having some trouble getting my program to make arrays of the right length. Our assignment is to make functions called "category1", "category2" and so on, all of which analyzes a char array and determines if the passed char array is in the specific category.
The "category" that I am having trouble with determines if the first third of the char array appears elsewhere in the whole array. Here's my code so far.

Code:

int Category4 (char s1[])
{
   int ndx, ndx2;
   char comp[strlen(s1)/3];

   for (ndx = 0; ndx < strlen(comp); ndx++) {
      comp[ndx] = s1[ndx];
   }

   for (ndx = strlen(comp); ndx < strlen(s1); ndx++) {
      if (s1[ndx] == comp[0]) {
         for (ndx2 = 0; ndx2 < strlen(comp); ndx2++) {
            if (comp[ndx2] != s1[ndx+ndx2]) {
               break;
            }
            if (ndx2 == strlen(comp)) {
               printf("%s is in category 4.\n", s1);
               return 1;
            }
         }
      }
   }

   return 0;
}

I pass a 6 character string each time, and the length that I get for the array I created in the function (comp) comes out to 5. Does anyone know why this is happening?