Qualcomm Software Engineer interview questions

1.Piece of code with static variable and whether the function is thread safe 2.Simple program on string 3.Big and little endian 4.negative of a number 5.Client & server communication using sockets 6.structure padding 7.Piece of code and find the errors. One was pass by reference, and the other was simple on range check. 8.Questions on resume and previous project work

What is the use of static variable? What is the use of extern ?