Correct usage of malloc and free for 2D array

I have a program that requires to create and delete a 2D array of variable size, hence the dynamic usage. However I wish to ask a simple question about the correct or recommended usage. For example, where should I reallocate the memory, should I simply free up the memory and use another allocation of memory i.e. memory allocation double etc should be done once...


or should be done in the loop


double **ptrBeadArrayOld = NULL;
ptrBeadArrayOld = (double **)malloc(BeadTotal * sizeof(double *));
for (i = 0; i< BeadTotal; i++)
free_2d(ptrBeadArrayOld);

or do I simply declare once?

double **ptrBeadArrayOld = NULL;

at the beginning of the program?? Thanks

Are you asking about whether you should determine the final size of the array and then allocate once, versus filling up the array and expanding when necessary?