When two pointers are subtracted, both must point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. This restriction exists because pointer subtraction in C produces the number of objects between the two pointers, not the number of bytes.
Similarly, comparing pointers can tell you gives the relative positions of the pointers in term of each other. Subtracting or comparing pointers that do not refer to the same array can result in erroneous behavior.
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The first incorrect assumption is that nums and strings arrays are necessarily contingent in memory. The second is that free_bytes is the number of bytes available. The subtraction will return returns the number of elements between next_num_ptr and strings.
Compliant Solution
In this compliant solution, the number of free elements is kept as a counter and adjusted on every array operation. It is also calculated in terms of free elements instead if bytes. This prevents further mathematical errors.
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