ggrr questions

• How to group "unlike" elements when iterating array (e.g.:{1,2,2,1,3,3,3,2,1,1} to {1,2}{2,1,3}{3}{3,2,1}{1})?
• why virtual void test()=00 is valid but virtual void test()=+0 and virtual void test()=-0 is not valid?
• Can I use the address of argc in main as random source?
• Why this sin cos look up table inaccurate when radian is large?
• How to check if a number < 1 is power of 2?
• Why doesn't the compiler automatically add or generate an include guard by default?
• What is the difference between Document and Value in rapidjson?
• How to call static method of other class in .html (not in .ts)?
• Is hardcode float precise if it can be represented by binary format in IEEE 754?
• how to handle arbitrary dimensional vector in c++?

ggrr answers