Why cyclic glucose is not a heterocyclic compounds if it consist Oxygen as a Heteroatom ?
Waylander is right, many sugars are heterocyclic compounds. While sugars such as glucose can exist in an open chain form, many of them are normally found in the form of six or five membered rings which consist of carbons and an oxygen.
Thus glucose fits the very definition of a heterocylic compound. It is important to keep in mind that any cylic (ring) compound where more than one element type is found in the atoms which make up the ring is a heterocylic compound.
For example S4N4, pyridine, ethylene oxide, glucose, 9-BBN and tetrahydrofuran are all heterocycles. They have very different chemistry to each other but they are all heterocylic.