A function_expression is simply a call to a function – passing any arguments as required by the function (E.g.   myfunction(1,2,b,b) ).       The result of the expression is the value returned by the function.       

Function expressions can be used anywhere in a expression where an rvalue is valid.

For example:

  a=myfunc(1,2) * yourfunc(3,2,3) - (a > compfunc(4,2));