qsort – quicker sort
void qsort(void *base, long nel, long width,
int (*compar)(void*, void*))
sorts an array into nondecreasing order.
The first argument is a pointer to the base of the data;
the second is the number of elements;
the third is the width of an element
the last is the name of a comparison routine
to be called with pointers
to elements being compared.
The routine must return
an integer less than, equal to, or greater than 0
according as the first argument is to be considered
less than, equal to, or greater than the second.