Fortran allows the intrinsic operator symbols to be extended to cases in which the operands are not of the usual intrinsic types defined by the standard.
For example, the (a user-defined type) or for operands of type logical with the interpretation provided by a user-supplied function subprogram.
In many cases, however, the value is assigned to a variable and that value can be used later in the program by referencing the variable.
Execution of the assignment statement causes the expression to be evaluated (by performing the computation indicated), and then the value of the expression is assigned to the variable on the left of the equal sign.
When the operator is an intrinsic operator such as with two numeric operands means that the two operands are added together.
For the user-defined operators, the interpretation is provided by a user-supplied function subprogram with a designation that this subprogram is to be used to define the operation.The rules for construction of expressions (the syntax rules) are the same for user-defined operators as for intrinsic operators.The general rule for evaluation of a Fortran expression states that any method that is mathematically equivalent to that provided by the construction and interpretation rules for the expression is permitted, provided the order of evaluation indicated by explicit parentheses in the expression is followed.Expressions often involve nonnumeric values, such as character strings, logical values, or structures; these also can be considered to be formulas that involve nonnumeric quantities rather than numeric ones.This chapter describes how valid expressions can be formed, how they are interpreted, and how they are evaluated.The following example shows an assignment statement: . Fortran has expressions of other types, such as logical, character, and derived type.Values of expressions of these other types can be assigned to variables of these other types.Intrinsic operators can be extended further by the programmer to operate on operands of types for which there are no intrinsic operations.Similarly, you can use defined unary and defined binary operators to operate on operands of types for which there are no previous definitions.In this chapter, however, certain terms from the standard have been changed to improve clarity.Fortran allows you to define data types, operators for these types, and operators for intrinsic types.