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

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 ?

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;

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;

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;

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;

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;

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

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;

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;

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;

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.

Further Reading and Exercises Further reading on web at home http://www.courseware.ust.hk/english/pascal_main/pascalfunction.html Homework Text book p.145, exercise 1-4 Think more, ask more, practice more,.. You would become an expert…