Fungsi dalam Pemrograman Komputer

1. Presented by :
Arinda Lailatul Karimah 4101412109
Septi Ratnasari 4101412082

2. Description
 A function is a group of statements that together
perform a task.
 Every Pascal program has at least one function which is
the program itself, and all the most trivial programs can
define additional functions.
 A function declaration tells the compiler about a
function's name, return type, and parameters. A
function definition provides the actual body of the
function.

3.  A function is similar to a procedure.
 Procedures accept data or variables when they are
executed. Functions also accept data, but have the ability
to return a value to the procedure or program which
requests it.
 Functions are used to perform mathematical tasks like
factorial calculations.
 A function :
1. begins with the keyword function
2. is similar in structure to a procedure
3. somewhere inside the code associated with the
function, a value is assigned to the function name
4. a function is used on the righth and side of an
expression
5. can only return a simple data type

4.  The only difference from the procedure is that the
function return a value at the end. Note that a procedure
cannot return a value. A function start and end in a
similar way to that of a procedure.
 If more than one value is required to be returned by a
module, we should make use of the variable parameter. A
function can have parameters too. If we change the sub-program
from procedure to a function, of the previous
program, there will be no difference in the output of the
program.
 Just make sure which one is best when we can to
implement a module. For example, if we don't need to
return any values, a procedure is more best. However if a
value should be returned after the module is executed,
function should be used instead.

5.  In Pascal, a function is defined using the function
keyword. The general form of a function definition is
as follows:
function name(argument(s): type1; argument(s): type2; ...):
function_type;
local declarations;
begin
...
< statements >
...
name:= expression;
end;

6.  A function definition in Pascal consists of a function
header, local declarations and a function body. The
function header consists of the keyword function and a
name given to the function.

7. Here are all the parts of a function:
1. Arguments:
The argument(s) establish the linkage between the calling
program and the function identifiers and also called the
formal parameters.
 A parameter is like a placeholder. When a function is
invoked, we pass a value to the parameter. This value is
referred to as actual parameter or argument. The
parameter list refers to the type, order, and number of
the parameters of a function. Use of such formal
parameters is optional. These parameters may have
standard data type, user-defined data type or subrange
data type.
 The formal parameters list appearing in the function
statement could be simple or subscripted variables,
arrays or structured variables, or subprograms.

8. 2. Return Type:
All functions must return a value, so all functions must
be assigned a type.
The function-type is the data type of the value the
function returns. It may be standard, user-defined scalar
or subrange type but it cannot be structured type.

9. 3. Local declarations:
local declarations refer to the declarations for labels,
constants, variables, functions and procedures, which are
application to the body of function only.

10. 4. Function Body:
The function body contains a collection of
statements that define what the function does.
It should always be enclosed between the
reserved words begin and end. It is the part of a
function where all computations are done.
There must be an assignment statement of the
type - name := expression; in the function body
that assigns a value to the function name. This
value is returned as and when the function is
executed. The last statement in the body must
be an end statement.

11.  Following is an example showing how to define a function in pascal:
(* function returning the max between two numbers *)
function max(num1, num2: integer): integer;
var
(* local variable declaration *)
result: integer;
begin
if (num1 > num2) then
result := num1
else
result := num2;
max := result;
end;

13. Function Declarations
 A function declaration tells the compiler about a function
name and how to call the function. The actual body of the
function can be defined separately.
 A function declaration has the following parts:
function name(argument(s): type1; argument(s): type2; ...):
function_type;
 For the above defined function max(), following is the
function declaration:
function max(num1, num2: integer): integer;

14.  Function declaration is required when we define a
function in one source file and we call that function in
another file. In such case we should declare the function
at the top of the file calling the function.

15. Calling a Function
 While creating a function, we give a definition of what
the function has to do.
 To use a function, we will have to call that function to
perform the defined task. When a program calls a
function, program control is transferred to the called
function.
 A called function performs defined task and when its
return statement is executed or when it last end
statement is reached, it returns program control back to
the main program.

16. To call a function we simply need to pass the required parameters
along with function name and if function returns a value then we
can store returned value. Following is a simple example to show
the usage:

18. Assigning a value to a function identifier
 The function's block definition must include a statement
that assigns a value to the function's identifier. This is
how a function gets a value that it can return to the
caller.
 If we omit this assignment statement, or the assignment
statement does not get executed as a result of
conditional statements in the function's code, then the
function returns an undefined or potentially random
value. If during the course of debugging a program we
find our functions returning erratic values, be certain
that the function identifier is correctly assigned a value.

19. Acceptable Function Return Values
 The data type that a function returns can be any of the
following:
a. Any ordinal value, including Boolean, Byte, Char, Smallint,
Integer, Word, Longint, and enumarated data types and
user defined sub range types.
b. Real, Single, Double, Extended and Comp data types,
c. Pointer values
d. Strings.
 Functions may not return records or sets, although they may
return pointers to records or sets.

20. Recursive Function
 Functions may call themselves. Such a function is called a
recursive function. A popular and simple example of a
recursive function is a function that computes the factorial
of a number. The factorial of a number n, is n * (n-1) * (n-2)
... until n reaches 1.

22. Important note:
The effect of short-circuit evaluation on functions
 By default, Turbo Pascal generates short-circuit evaluation code, so it is
possible that a function may not be called within a particular expression.
For example, consider a function defined as:
function ValueInRange ( X1 : Integer ) : Boolean;
begin
...
if X1 > 0 then
ValueInRange := True
else
ValueInRange := False;
if X1 < LowestCoordinate then
LowestCoordinate := X1;
end;

23.  In this function, a global variable LowestCoordinate may
have its value changed during the course of execution. If
this function is called in an expression such as,
if (X1<>X2) and ValueInRange(X1) then ...

24. Function as Parameter
 A function may itself be passed to another function as a
parameter value. To pass a requires that a type
declaration define a procedure type that matches the
appropriate function header. This type becomes the
parameter type used in the procedure parameter list.

26. Fungsi Add

27. Fungsi Max-ab

28. Fungsi Genap - Ganjil

29. Fungsi Midpoint

30. Fungsi Phytagoras

31. Fungsi Luas
Segitiga

32. Fungsi Luas
Persegi Panjang

33. Fungsi Volume
Balok