why changes in cash doesn't include under operating service in cash flow statement?

Question

changes in cash is put after the the 3 categories (operating, investing and financing).

Answer 1

The changes in cash and cash equivalents (CCE) are not "put" after the 3 categories. Rather, CCE is arrived at from working out the inflows and outflows in the 3 categories. The net inflow or outflow of the 3 categories gives you the net increase or decrease in CCE for the year, that's why you add it to beginning CCE to get ending CCE.