Functions, subroutines, and statement functions are user-written subprograms that perform computing procedures. The computing procedure can be either a series of arithmetic operations or a series of Fortran statements. A single subprogram can perform a computing procedure in several places in a program, to avoid duplicating a series of operations or statements in each place.
The following table shows the statements that define these subprograms, and how control is transferred to the subprogram:
| Subprogram | Defining Statements | Control Transfer Method |
|---|---|---|
| Function | FUNCTION or ENTRY | Function reference 1 |
| Subroutine | SUBROUTINE or ENTRY | CALL statement 2 |
| Statement function | Statement function definition | Function reference |
|
1 A function can also be invoked by a defined operation
(see Section 8.9.4).
2 A subroutine can also be invoked by a defined assignment (see Section 8.9.5). | ||
A function reference is used in an expression to invoke a function; it consists of the function name and its actual arguments. The function reference returns a value to the calling expression that is used to evaluate the expression.
The following topics are described in this section:
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