saniati@teknokrat.ac.id or saniati.8820@gmail.com

1. Algorithm and Programming
Saniati
saniati@teknokrat .ac.id

2. Objective of
this session
 Student able to know definition dan theories of function.
 Student able to use and create functions.
 Student able to know theories of variable scope.
 Student able to identify the scope of variable.

3. Function
• A function is a block of code that performs a task
• A function is a type of procedure or routine.
• Some program contains at least one function: main()
• Why use functions?
▫ Allow programmer to avoid duplicating code
▫ Allow programs to be broken into manageable
tasks
• Two categories of function:
▫ Value-returning functions
▫ Void functions

4. Value –
Returning
Function
• A value-returning function returns precisely one value
after completing its assigned task.
▫ Usually returned to the statement that called function
 Typically, statement displays return value, uses it in a
calculation, or assigns it to a variable
▫ Some value-returning functions
 E.g., pow(3,2)

5. Value –
Returning
Function
• A value-returning function returns precisely one value
after completing its assigned task.
▫ Usually returned to the statement that called function
 Typically, statement displays return value, uses it in a
calculation, or assigns it to a variable
▫ Some value-returning functions
 E.g., pow(3,2)

6. Example
int

7. Void Function
void sayHello(string name)
{
write (“Halloooo “ + name );
}
Without
Return

8. Components
of Function
Function
Header
Function
Body

9. Function
Header
• Function header: first line in a function definition
▫ Does not end with a semicolon
▫ Begins with returnDataType
▫ Next comes the name of the function
 Naming rules are the same as for naming variables
 Name usually begins with a verb
▫ Also has an optional parameterList enclosed in ()
 Lists data type and name of formal parameters
 Formal parameters store the information passed to the function when it is
invoked
Formal
Parameter

10. Function
Body
• Function body contains instructions the function
follows to perform its assigned task
▫ Begins with { and ends with }
▫ The last statement is usually return expression;
 expression represents the value the function returns to the statement
that called it
▫ return statement alerts computer that the
function has completed its task
 Data type of expression must agree with the returnDataType specified
in function header

11. 11

12. Call a function
(1)
void main(){
int a, b, c;
b = 5;
c = sum (a, b);
write (c);
}
int sum (int num1, int num2)
{
int result;
result = num1 + num2;
return (result);
}
Calling function
Variable, get the
return of function

13. Call a function
(2)
void main(){
int a , b, c;
a = 9; b = 5;
c = sum (a, b);
write (c);
}
int sum (int num1, int num2)
{
int result;
result = num1 + num2;
return (result);
}
Actual Parameter

14. Passing
Information to
a Function
• Items passed to a function are actual perameters/
arguments
▫ Can be a variable, named constant, literal constant, or
keyword
 You can pass a variable:
 by value (a copy of the value is passed), or
 by reference (the variable address is passed)
▫ Examples
 calcRectangleArea(2, 3)
 calcRectangleArea(length, width) pass by value

15. Using a
Function
Prototype
• If a function definition appears below main(), you must
enter a function prototype above main()
▫ Prototype specifies function’s name, data type of
return value and of each formal parameter

16. 16

17. The Scope
and Lifetime
of a Variable
• A variable’s scope indicates where
in the program it can be used
▫ Local or global
 Local variables are declared within a
function or appear in a function’s
parameterList
 Global variables are declared outside
of any function and remain in memory
until program ends
 Avoid using global variables in your
programs
• A variable’s lifetime indicates how
long it remains in memory

18. Summary
 A function is a block of code that performs a task.
 Categories of function: Value-returning functions
& Void functions
 Components of function : Header Function &
Body Function
 Types of Parameter : Formal & Actual
 Next  Recursive Function