How do you add a null pointer to a char array?

I have a char array that takes in words, char myarray[max_words][max_chars] and I want to add a null pointer (char *)0 to it. I am not sure how to do that. I have been getting compiling errors saying incompatible types.

You can't because you don't have an array of pointers. You have an array of characters which is max_words*max_chars big.

If you are trying to flag the end of the list, you could use an empty string. You create an empty string by putting a null character, aka ", in the first position(the null character is NOT the same things as NULL in C, although it is in C++):

myarray[x][0] = ";
Can also be written as:
myarray[x][0] = 0;
And in C++, but not C, as:
myarray[x][0] = NULL;

The other alternative is to make your array an array of pointers:
char *myarray[max_words];
Then you can write:
myarray[x] = NULL;

But then you will have to allocate memory for each new string in the array, and worry about freeing it later.