This means lastZ and z are structures.

> lastZ = z; // tdis initialization

I believe this make the structure lastZ point to the structure z. This
is different than using:

lastZ.r = z.r;
lastZ.i = z.i;

which moves the contents of z to lastZ, but leaves the pointers pointing
to separate structures.

These are structs not pointers to structs so the members should be copied. I should have given the type definition for complex.

typedef struct complexStruct

{

double r;

double i;

} complex;

so doing:

complex lastZ;

is the same as:

struct complexStruct lastZ;

and lastZ = z; should copy the members not copy a pointer.

I hope this is right. I have the same thing in dozens of places.