What are these symbol known <,>,=<,=>,! <,== ?

Answer 1

< less then
> more then
=< equal or less then
=> equal or greater then
!< not less then
== equal to

Answer 2

Those are Relational operators.
For more info on operators in C language, check this out:

https://www.studytonight.com/c/operators-in-c.php

Answer 3

'!' means 'not', so:
!=
means:
not equal
and:
!variablename
is equivalent to:
variablename != 0