8.137 ISNAN — Test for a NaN

Description:

ISNAN tests whether a floating-point value is an IEEE Not-a-Number (NaN).

Standard:

GNU extension

Class:

Elemental function

Syntax:

ISNAN(X)

Arguments:

X	Variable of the type REAL.

Return value:

Returns a default-kind LOGICAL. The returned value is TRUE if X is a NaN and FALSE otherwise.

Example:

          program test_nan
            implicit none
            real :: x
            x = -1.0
            x = sqrt(x)
            if (isnan(x)) stop '"x" is a NaN'
          end program test_nan