==                       Equality operator

 exp1 == exp2            Test for exp1 equal to exp2
 exp1, exp2              any expression

    == is a relational  operator, yielding a value  of either TRUE, if  the
    expressions have  the same  value; or  FALSE if  the expressions do not
    have the same  value.  For  string or regular  expression operands, the
    strings are compared according to  the collating sequence.  Here  is an
    example:

           if ( number == guess )
               ...
           do  {
               ...
           } while ( ans == 'y' );

!=                       Inequality operator (Not Equal)

 exp1 != exp2            Test for exp1 not equal to exp2
 exp1, exp2              any expression

    != is a  relational operator, yielding  a value of  TRUE if exp1  has a
    different value than exp2; or FALSE if exp1 has the same value as exp2.
    For  string  operands,  the  strings  are  compared  according  to  the
    collating sequence.  Example:

           if ( number != guess )
               ...
           do  {
               ...
           } while ( ans != 'n' );