pseudocode
TYPE CarRecord
DECLARE VehicleID : STRING
DECLARE Registration : STRING
DECLARE DateOfRegistration : DATE
DECLARE EngineSize : INTEGER
DECLARE PurchasePrice : CURRENC
ENDTYPE
// declare a variable
DECLARE ThisCar : CarRecord
python code
class CarRecord: # declaring a class without other methods
def __init__(self): # constructor
self.VehicleID = ""
self.Registration = ""
self.DateOfRegistration = None
self.EngineSize = 0
self.PurchasePrice = 0.00
ThisCar = CarRecord() # instantiates a car record
ThisCar.EngineSize = 2500 # assign a value to a field
Car = [CarRecord() for i in range(100)] # make a list of 100 car records
Car[1].EngineSize = 2500 # assign value to a field of the 2nd car in list
Java code
class CarRecord {
String vehicleID;
String registration;
String dateOfRegistration;
int engineSize;
double purchasePrice;
public CarRecord() { // declare a constructor without other methods
vehicleID = "XX";
registration = "";
dateOfRegistration = "01/01/2010";
engineSize = 0;
purchasePrice = 0.00;
}
}
CarRecord thisCar = new CarRecord(); // instantiates a car record
thisCar.engineSize = 2500; // assign a value to a field
CarRecord[] car = new CarRecord[100]; // declare an array of car record type
car[2] = new CarRecord(); // instantiate a car
car[2].engineSize = 2500; // assign a value to a field of 2nd car in array
| Structured English | Pseudocode |
|---|---|
| Create a file and open it for writing | OPENFILE |
| Open a file in append mode | OPENFILE |
| Open a file for reading | OPENFILE |
| Open a file for random access | OPENFILE |
| Close a file | CLOSEFILE |
| Write a record to a file | PUTRECORD |
| Read a record from a file | GETRECORD |
| Move to a specific disk address within the file | SEEK |
| Test for end of file | EOF( |
// Saving content of array
OPENFILE CarFile FOR WRITE
FOR i ← 1 TO MaxRecords
PUTRECORD CarFile, Car[i]
NEXT i
CLOSEFILE CarFile
// Restoring contents of array
OPENFILE CarFile FOR READ
FOR i ← 1 TO MaxRecords
GETRECORD CarFile, Car[i]
NEXT i
CLOSEFILE CarFile
import pickle # this library is required to create binary files
Car = [CarRecord() for i in range(100)]
CarFile = open('CarFile.DAT', 'wb') # open file for binary write
for i in range(100): # loop for each array element
pickle.dump(Car[i], CarFile) # write a whole record to the binary file
CarFile.close() # close file
CarFile = open('CarFile.DAT', 'rb') # open file for binary read
Car = [] # start with empty list
while True: # check for end of file
Car.append(pickle.load(CarFile)) # append record from file to end of list
CarFile.close()
// writing records to a file:
import java.io.DataOutputStream;
import java.io.FileOutputStream;
import java.io.EOFException;
import java.io.FileInputStream;
import java.io.FileOutputStream;
try
{ // set up file stream and link to file name
FileOutputStream fos = new FileOutputStream("CarFile.DAT");
// link file stream to data stream
DataOutputStream dos = new DataOutputStream(fos);
for (int i = 1; i < 100; i++) // loop for each array element
{
dos.writeUTF(car[i].vehicleID); // write a field to the file
dos.writeUTF(car[i].registration); dos.writeInt(car[i].engineSize);
dos.writeUTF(car[i].dateOfRegistration);
dos.writeDouble(car[i].purchasePrice);
}
dos.close(); // close data stream
}
catch (Exception x)
{
System.out.println("IO error");
}
// reading records back into array:
CarRecord[] car = new CarRecord[100];
try
{ // set up file stream and link to file name
FileInputStream fis = new FileInputStream("CarFile.DAT");
// link file stream to data stream
DataInputStream dis = new DataInputStream(fis);
int i = 1;
while (true) // loop for each array element
{
thisCar = new CarRecord();
thisCar.vehicleID = dis.readUTF(); // read fields from the file
thisCar.registration = dis.readUTF();
thisCar.engineSize = dis.readInt();
thisCar.dateOfRegistration = dis.readUTF();
thisCar.purchasePrice = dis.readDouble();
car[i] = thisCar; // assign record to next array element
i += 1;
}
}
catch (EOFException x)
{
System.out.println("End of File reached");
}
catch (Exception x)
{
System.out.println(x); // output error message
}
pseudocode
// Saving a record
OPENFILE CarFile FOR RANDOM
Address ← Hash(ThisCar.VehicleID)
SEEK CarFile, Address
PUTRECORD CarFile, ThisCar
CLOSEFILE CarFile
// Retrieving a record
OPENFILE CarFile FOR RANDOM
Address ← Hash(ThisCar.VehicleID)
SEEK CarFile, Address
GETRECORD CarFile, ThisCar
CLOSEFILE CarFile
python
import pickle # this library is required to create binary files
ThisCar = CarRecord()
CarFile = open('CarFile.DAT','rb+') # open file for binary read and write
Address = hash(ThisCar.VehicleID)
CarFile.seek(Address)
pickle.dump(ThisCar, CarFile) # write a whole record to the binary file
CarFile.close() # close file
// to find a record from a given VehicleID:
CarFile = open('CarFile.DAT','rb') # open file for binary read
Address = hash(VehicleID)
CarFile.seek(Address)
ThisCar = pickle.load(CarFile) # load record from file
CarFile.close()
java
CarRecord thisCar;
int recordSize = 50;
try // set up a file with 100 dummy records
{
RandomAccessFile writer = new RandomAccessFile("CarFile.DAT", "rw");
for (int i = 1; i < 100; i++) // loop for each array element
{
thisCar = new CarRecord();
thisCar.vehicleID = "A" + i;
writer.seek(i * recordSize);
writer.writeUTF(thisCar.vehicleID);
writer.writeUTF(thisCar.registration);
writer.writeUTF(thisCar.dateOfRegistration);
writer.writeInt(thisCar.engineSize);
writer.writeDouble(thisCar.purchasePrice);
}
writer.close();
} catch (IOException x)
{
}
//to find a record from a given VehicleID:
try {
RandomAccessFile writer = new RandomAccessFile("CarFile.DAT", "rw");
RandomAccessFile reader = new RandomAccessFile("CarFile.DAT", "r");
reader.seek(hash(vehicleID));
thisCar = new CarRecord();
thisCar.vehicleID = reader.readUTF();
thisCar.registration = reader.readUTF();
thisCar.engineSize = reader.readInt();
thisCar.dateOfRegistration = reader.readUTF();
thisCar.purchasePrice = reader.readDouble();
reader.close();
}
catch (IOException x)
{
}
Run-time errors can occur for many reasons. Some examples are division by zero, invalid array index or trying to open a non-existent file. Run-time errors are called ‘exceptions’. They can be handled (resolved) with an error subroutine (known as an ‘exception handler’), rather than let the program crash.
TRY
<statementsA>
EXCEPT
<statementsB>
ENDTRY
Any run-time error that occurs during the execution of <statementsA> is caught and handled by executing <statementsB>.
There can be more than one EXCEPT block, each handling a different type of exception.
Sometimes a FINALLY block follows the exception handler.
Python distinguishes between different types of exception, such as:
Java distinguishes between different types of exception, such as:
python
NumberString = input("Enter an integer: ")
try:
n = int(NumberString)
print(n)
except:
print("This was not an integer")
java
import java.util.Scanner;
{
public static void main(String[] args)
{
Scanner console = new Scanner(System.in);
try
{
System.out.print("Enter an integer: ");
int n = console.nextInt();
System.out.println(n);
}
catch(Exception e) // catches any exception
{
System.out.println("This was not an integer");
}
}
}