Pascal Lecture notes – Adams

It’s useful to know how to comment in a language

(* *) shows the delimiters for Pascal comments

{ }

Pascal is NOT case sensitive

Pascal only guarantees identifiers are unique if they are different from all other identifiers in the first 8 characters

Pascal has both reserved words (35 or 36) and predefined terms

INPUT statement

READ (X); (* is equivalent to saying *) READ (input, X);

READLN (X) (* is equivalent to saying *) READLN (input, X);

READ (file, X) (* means read from the file known as file *)

• The difference between read and readln is that readln goes to the next line after it executes where as read stops where it is

OUTPUT statement

WRITE (X); (* is equivalent to saying *) WRITE (output, X);

WRITELN (X); (* is equivalent to saying *) WRITELN (output, X);

• Write and writeln can also be used with files.
• The difference between write and writeln is that writeln moves the print head to the next line after it executes and write stops where it is.

NOTE: you will need to distinguish between the internal and the external file names. The one used in the READ, READLN, WRITE, and WRITELN statements is the internal name not the diskfile name.

ITERATION statement

FOR loop is a counted loop. It executes a fixed number of times

FOR loopControlVariable := intialValue TO endingValue DO

SingleStatement;

FOR loopControlVariable := intialValue TO endingValue DO

BEGIN MultipleStatements;

END;

FOR loopControlVariable := initialValue DOWNTO endingValue DO

SingleStatement;

WHILE loop is executes until a condition is met. It will not be executed at all if the condition is not true on entry to the loop. (Pre-test loop)

WHILE (true) DO

Do this one thing;

WHILE (true) DO

BEGIN

END;

(* the begin end pair of reserved words makes a group of statements equivalent syntactically to a single statement *)

REPEAT … UNTIL loop executes until a condition is met. It always executes at least once because it’s a post test loop.

ASSIGNMENT statement

x:=y;

NOTE: in Pascal, the semi-colon is a statement separator not a statement terminator.

SELECTION statement

IF (condition) THEN

singleThingToDo;

IF (condition) THEN

BEGIN

multipleThingsToDo

END;

IF statements can be nested.

IF (condition) THEN

singleThingToDo (* NEVER EVER A SEMICOLON BEFORE AN ELSE *)

ELSE

singleThingToDo;

CASE is a multi-alternative selection statement

CASE identifier OF

Value : action; (* action can be single or multiple statements *)

Value2 : action2;

Value3..Value5 : action3;

Value4, value7, value12 : action4;

END; (* of case statement *)