1. Pascal Subprogram Procedure Function Build in Function (e.g. Sin(x))
Self-defined Function (out of syllabus)

2. A Pascal Program program Scope; var Num1, Num2, Sum : integer; begin
Sum := Num1 + Num2;
writeln( 'The sum is ', Sum )
end.
What is the sample output ?

3. Using Procedure procedure FindSum; program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum;
writeln( 'The sum is ', Sum )
end.
What is “FindSum” ?
procedure FindSum;
begin
Sum := Num1 + Num2
end;

4. Global Variables procedure FindSum; begin Sum := Num1 + Num2 end;
How it works ?
program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum;
writeln( 'The sum is ', Sum )
end.
procedure FindSum;
begin
Sum := Num1 + Num2
end;

5. Local Variables procedure FindSum; program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum;
writeln( 'The sum is ', Sum )
end.
Which is the
local variable?
procedure FindSum;
var Sum : integer;
begin
Sum := Num1 + Num2
end;

6. Parameter Passing procedure FindSum( A, B:integer; program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum( Num1,Num2,Sum );
writeln( 'The sum is ', Sum )
end.
procedure FindSum( A, B:integer;
var C:integer);
begin
C := A + B
end;

7. Formal & Actual Parameters
program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum( Num1,Num2,Sum );
writeln( 'The sum is ', Sum )
end.
How the data flows in and flows out?
procedure FindSum( A, B:integer;
var C:integer);
begin
C := A + B
end;

8. Formal & Actual Parameters
program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum( Num1,Num2,Sum );
writeln( 'The sum is ', Sum )
end.
procedure FindSum( A, B:integer;
var C:integer);
begin
C := A + B
end;
Formal vs. actual parameter

9. Formal & Actual Parameters
If I forget to type var…
program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum( Num1,Num2,Sum );
writeln( 'The sum is ', Sum )
end.
procedure FindSum( A, B:integer;
var C:integer);
begin
C := A + B
end;

10. Value & Variable Parameters
program Scope;
var Num1, Num2, Sum : integer;
begin
Num1 := 10;
Num2 := 15;
FindSum( Num1,Num2,Sum );
writeln( 'The sum is ', Sum )
end.
Value vs Variable parameter
procedure FindSum( A, B:integer;
var C:integer);
begin
C := A + B
end;

11. General format of a procedure
procedure heading
procedure < name of procedure >
(formal parameter list:data type) ;
local declarations part
const < constant definitions > ;
type < type definitions > ;
var < variable declarations > ;
statement part
begin
< statements >;
end;

12. Beware of ….
check that a procedure must be declared and placed in the proper position of a program
remember that a procedure must be ended with the reserved word END and a semicolon.
match the type and order of the actual parameters to the corresponding formal parameters
make sure that an actual parameter is a variable when corresponding to a variable parameter.

13. Further Reading and Exercises
Further reading on web at home
Homework
Text book p.145, exercise 1-4
Think more, ask more, practice more,..
You would become an expert…