GNVQ Advance IT

• an editor for creating your source code
• a compiler to check the syntax of your program, to report and identify errors and to produce object code
• a linker to produce executable code
• a "de-bug" facility to help find run-time errors
• a file manager to allow you to quickly save, retrieve and print your source files.

 

The stages in developing a Pascal program are essentially the same as for any other language:

1. Understand the Problem
2. Design the solution to the problem
3. Convert the solution into Pascal, that is, write the code in the Pascal language
4. Remove any syntax errors from your program - this involves a cycle of compiling the program and correcting any errors until the program compiles successfully.
5. Link the program to include any library routines
6. Test the program until all errors - compilation, logical and run-time have been removed

Variable Declaration
Variables are those items of data which can be changed by the program instructions.  To distinguish between these data items they are given names.  These names or identifiers  can be a combination of letters and or numbers, provided the name begins with a letter.  However, they must not be the same as a Pascal reserved word.  All variables must be declared in Pascal (though this is not necessarily true of other languages).

Each variable declaration consists of:
variable name: data type; comment

For example:

VAR
 mileage: INTEGER;{distance to work}
 allowance: REAL; {travel allowance per mile}
 reply: CHAR;{answer Y or N}
 expenses: REAL; {monthly travelling expenses}
 name: ARRAY[0..10] of CHAR;{name of max 10 char’s]

Constant declaration
In many programs there will be data values that do not change, but remain constant throughout the program execution.  An example might be Value Added Tax - VAT, or the value of Pi.  These could be declared thus:

CONST
 vat = 17.5;{current rate of VAT}
 pi = 3.14159;{pi to 5 decimal places}
 

 How do we put this in a program?
There is a set order for declaring constants and variables in a Pascal program.  The format for data declaration at the beginning of a program is:

PROGRAM name;
{begin declarations}
CONST
VAR
{end declarations}
 

An example from a bicycle hiring program might look as follows.

PROGRAM bike;

{begin declarations}
CONST
 summer = 10.0;{hire charge April - October}
 winter = 5.0;{hire charge Nov - March

VAR season: CHAR;{A - summer, B - winter}
 days: REAL;{number of days of hire}
 charge: REAL;{cost of hiring bike}
{end declarations}

Type this code into the Pascal editor, compile and correct any syntax errors.

Task: 2