You have to free() the allocated memory in exact reverse order of how it was allocated using malloc().
Note that You should free the memory only after you are done with your usage of the allocated pointers.
memory allocation for 1D arrays:
buffer = malloc(num_items*sizeof(double));
memory deallocation for 1D arrays:
free(buffer);
memory allocation for 2D arrays:
double **cross_norm=(double**)malloc(150 * sizeof(double *));
for(i=0; i<150;i++)
{
cross_norm[i]=(double*)malloc(num_items*sizeof(double));
}
memory deallocation for 2D arrays:
for(i=0; i<150;i++)
{
free(cross_norm[i]);
}
free(cross_norm);