If I travel to China then Tibet ( with Tibet visa )and back to China do I need a double entry visa

You don't need a double entry visa, Tibet is a part of China, you can use a single-entry China visa to visit tibet and other cities in Mainland China, the Tibet Entry Permit is also required besides a single-entry China visa.

Hong Kong and Macau are special administrative regions, they apply different exit and enter controls from Mainland China. If you go to Mainland China, then go to Hong Kong/Macau, then return to Mainland China, you need a double entry visa.