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int nums[SIZE];
char *stringsc_str[SIZE];
int *next_num_ptr = nums;
int free_bytes;

/* increment next_num_ptr as array fills */

free_bytes = stringsc_str - (char **)next_num_ptr;

The first incorrect assumption is that the nums and strings c_str arrays are necessarily contiguous in memory. The second is that free_bytes is the number of bytes available. The subtraction returns the number of elements between next_num_ptr and strings c_str.

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 of bytes. This practice prevents further mathematical errors.

int nums[SIZE];
char *stringsc_str[SIZE];
int *next_num_ptr = nums;
int free_bytes;

/* increment next_num_ptr as array fills */

free_bytes = (&(nums[SIZE]) - next_num_ptr) * sizeof(int);

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