8.4 Functions, Subroutines, and Statement Functions

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 8.8.4).
[2] A subroutine can also be invoked by a defined assignment (see Section 8.8.5).

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 which is used to evaluate the expression.

The following topics are described in this section:

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