Assigns the value of the expression to the variable.
  Arithmetic/Logical/Character assignment takes the form:

     v = e

     v  Is the name of a scalar or array of intrinsic
        or derived type (with no defined assignment).
        The array cannot be an assumed-size array, and
        neither the scalar nor the array can be declared
        with the PARAMETER or INTENT(IN) attribute.

     e  Is an expression of intrinsic type or the same
        derived type as "v". Its shape must conform with
        "v". If necessary, it is converted to the same kind
        type as "v".

  Before a value is assigned to the variable, the expression part of
  the assignment statement and any expressions within the variable
  are evaluated.  No definition of expressions in the variable can
  affect or be affected by the evaluation of the expression part of
  the assignment statement.

  NOTE:  When the run-time system assigns a value to a scalar integer
  or character variable and the variable is shorter than the value
  being assigned, the assigned value may be truncated and significant
  bits (or characters) lost.  This truncation can occur without
  warning, and can cause the run-time system to pass incorrect
  information back to the program.

  If the variable is a pointer, it must be associated with a
  definable target.  The shape of the target and expression must
  conform and their types and kind type parameters must match.