subprogram in pascal
DESCRIPTION
SUBPROGRAM IN PASCAL. PROCEDURE Lecture 5 CS1023. Example of Procedure using pass-by-value. program doubleTrouble; procedure double (num : integer); begin num := num * 2; writeln('The double is ', num); end; var number : integer; begin number := 3; double(number); - PowerPoint PPT PresentationTRANSCRIPT
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SUBPROGRAM IN PASCAL
PROCEDURE
Lecture 5
CS1023
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Example of Procedureusing pass-by-value
program doubleTrouble;procedure double (num : integer);begin
num := num * 2;writeln('The double is ', num);
end;var
number : integer;begin
number := 3;double(number);writeln('The number is ', number);
end.{What is the output? }
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Pass by reference
The default for procedure parameters is pass by value.
Sometimes, we want the procedure to modify the actual parameter.
We use pass by reference to pass the memory location of the actual parameter to the procedure.
Use the key word, var, in the formal parameter to indicate that the parameter is pass-by-reference.
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Exampleprogram doubleTrouble;procedure double2(var num : integer);begin
num := num * 2;writeln('The double is ', num);
end;var
number : integer;begin
number := 3;double2(number);writeln('The number is now ', number);
end.
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Execution of doubleTrouble
When double2( ) is called, the address of number is passed to the parameter, num.
num and number label the same location in memory.
When the value of num changes, the value of number also changes (because they label the same memory location).
What is the output?
numbernum
4000
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More than one parameterprogram CalcCube;procedure Cube( n : integer; var result :
integer);begin
result := n * n * n;end;var
number : integer;answer : integer;
beginwriteln('Enter a number: ');readln(number);Cube(number, answer);writeln('The cube of ', number, ' is ', answer);
end.
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Matching up parameters
Actual parameters are matched up in order with the formal parameters.
In the previous example, the value of number is passed to n (pass-by-value).
The address of answer is passed to result (pass-by-reference).
number nanswer
result
6000
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Local Variables for Procedures
Procedures can have variables in addition to parameters.
A variable declared within a procedure definition is local to that procedure.
A local variable is invisible to other procedures and the main program.
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Example: Volume of a Cylinderprogram volumeFinder;procedure WriteCylinderVolume( r, h : real);var
volume : real; {local variable for WriteCylinderVolume}
beginvolume := 3.14159 * r * r * h;writeln( 'The volume is ', volume);
end;var
radius, height : real; {variables for main program}
beginwriteln('Enter the radius and the height: ');readln(radius);readln(height);WriteCylinderVolume(radius, height);
end.
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Example: Swap two variables
Procedure swap(var x : integer, var y: integer)
Vartemp: integer;
Begintemp:= x;x:= y;y:= temp;
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Exercises• Tuliskan prosedur PUTAR3BIL untuk memutar tiga buah
bilangan integer dengan menggunakan prosedur swap. Contoh:– Jika a berisi 1, b berisi 2, dan c berisi 3, maka hasilnya:
a berisi 3, b berisi 1, dan c berisi 2.• Tuliskan prosedur untuk menyederhanakan bilangan
rasional atau pecahan berbentuk a/b dimana a dan b adalah bilangan bulat dan a<b. contoh: jika diberikan pecahan 5/10 ½.
• Tuliskan algoritma untuk menjumlahkan dua buah matriks. Ukuran matriks MxN diberikan oleh pengguna. Algoritma tersebut dibangun dari tiga prosedur, yaitu prosedur masukan dua buah matriks, prosedur menjumlahkan kedua matriks tersebut, dan prosedur menampilkan hasil penjumlahannya.
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Exercises
• Tuliskan prosedur untuk menyederhanakan pecahan x/y menjadi bentuk a b/c dimana x dan y adalah bilangan bulat dan x > y. Contoh: 14/5 24/5
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Referensi
• Liem Inggriani, Diktat kuliah IF223 Algoritma dan Pemrograman, Jurusan Teknik Informatika ITB, 1999
• DT/266/1, Programming Language, Departement of Computer Science.
• Data structure, CSCI 262, Lecture 2 Classes and Abstract Data Types