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In Fortran, calculations are specified by writing expressions.Expressions look much like algebraic formulas in mathematics, particularly when the expressions involve calculations on numerical values.As with operators, the programmer can extend the meaning of assignment to types not defined intrinsically and can redefine assignment for two objects of the same derived type. In addition, arrays and pointers each have special forms of assignment statements called masked array assignment and pointer assignment, respectively.
This chapter describes using arrays and pointers in the following contexts: The result obtained from the evaluation of an expression can be used in many ways.
For example, it can be printed or passed to a subprogram.
The formation rules for expressions imply that the defined unary operators have highest precedence of all operators, and defined binary operators have the lowest precedence of all operators.
When they appear in a context where two or more of these operators of the same precedence are adjacent, the operands are combined with their operators in a left-to-right manner, as is the case for the familiar operates on operands of type integer as well as real and complex.
When the operator is an intrinsic operator such as with two numeric operands means that the two operands are added together.
Fortran Array Assignment
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 formal (BNF) rules for forming expressions imply an order for combining operands with operators.
These rules specify that expressions enclosed in parentheses are combined first and that, for example, the multiply operator , respectively.
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.