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 reference1 |
Subroutine |
SUBROUTINE or ENTRY |
CALL statement2 |
Statement function |
Statement function definition |
Function reference |
1 A function can also be invoked by a defined operation (see Defining Generic Operators). 2 A subroutine can also be invoked by a defined assignment (see Defining Generic Assignment). |
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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.