Pascal statements

Statement separators

Statements are separated by semicolons, not ended by them: the semicolon is written between two statements. A semicolon before end, until, else is allowed, because it ends with an empty statement. A semicolon directly before else is an error, because it would end the if statement before its else. Statements may have a label in front: Done: WriteLn('x');.

Assignment and calls

X := 3;                    { assignment }
A[I].Name := 'x';          { to a field of an element }
Count += 1;                { with {$COPERATORS ON} (Free Pascal): += -= *= /= }
Result := Left + Right;    { the value a function returns }
Writeln('hello');          { a procedure call }
Obj.Method(1, 2);          { a method call }
Add(5);                    { a function call whose result is dropped (extended syntax, {$X+}) }

The assignment operator is :=. The left side is a variable, a function name (inside that function, in ISO 7185 and Turbo Pascal to give the result), or Result. A procedure call is its name with arguments in parentheses; with no parameters the parentheses are optional. A function may be called as a statement and its result ignored when extended syntax is on (the default in Delphi and Free Pascal).

Compound statement

begin
  A := 1;
  B := 2
end

begin … end groups statements into one. It is the body of every routine and the main program.

if

if X > 0 then
  WriteLn('positive')
else if X < 0 then
  WriteLn('negative')
else
  WriteLn('zero');

The condition is a Boolean expression. There is no semicolon before else. In a chain, an else belongs to the nearest if that has none (the dangling else); use begin … end to change that.

case

case Ch of
  'a'..'z': WriteLn('lower');
  'A'..'Z': WriteLn('upper');
  '0'..'9', '_': WriteLn('word');
else
  WriteLn('other');            { Turbo Pascal, Delphi, Free Pascal; otherwise in ISO 10206 and Free Pascal }
end;

The selector is an ordinal expression. Each arm has one or more constants or ranges, separated by commas, then a colon and a statement. The arms must not overlap. ISO 7185 has no else: a selector value with no arm is an error. Turbo Pascal and later add else, and Extended Pascal adds otherwise (Free Pascal accepts it too). A semicolon is allowed before else in a case.

for

for I := 1 to 10 do Sum := Sum + I;
for I := 10 downto 1 do Write(I, ' ');
for C := 'a' to 'z' do Write(C);
for Colour := Red to Blue do ...

for Item in List do Process(Item);        { Delphi and Free Pascal }
for Ch in 'text' do Write(Ch);
for var I := 0 to 9 do ...               { Delphi 10.3 and later: the variable is declared here }

The control variable is an ordinal variable that, in ISO 7185 and in Delphi, must be local to the routine. The limits are evaluated once, before the loop. The loop body must not change the control variable.
With to the variable counts up, with downto it counts down. If the limits make the loop empty, the body does not run. After a normal end the value of the variable is undefined in ISO 7185 and most dialects.
for … in (Delphi, Free Pascal) loops over the elements of an array, a set, a string, an enumeration, or an object that provides an enumerator: a GetEnumerator method returning an object with MoveNext and Current.

while and repeat

while not Eof(F) do
  ReadLn(F, Line);

repeat
  Read(Ch);
until Ch = #13;

while tests its condition before each pass, so the body may never run. repeat … until runs the statements between the two words at least once and stops when the condition becomes true; it needs no begin and end to hold several statements.

with

with Rec do
begin
  X := 1;       { Rec.X }
  Y := 2;       { Rec.Y }
end;
with A, B do ...    { the same as with A do with B do }

with makes the fields and methods of a record, object, class or interface directly visible in the statement. A name in the body is looked for in the innermost with first, which can hide a variable of the same name outside it.

goto

goto Label jumps to a statement that has that label in the same block (see Declarations). Structured programming avoids it, and it is mainly used to leave deeply nested loops.

exit, break, continue, halt

Exit leaves the current routine (or the main program or unit initialisation). Exit(Value) sets Result and leaves (Delphi 2009 and later, Free Pascal).
Break leaves the innermost for, while or repeat loop. Continue skips to its next pass. Turbo Pascal 7, Delphi and Free Pascal have these two.
Halt or Halt(Code) ends the program with an exit code. RunError(N) ends it with a run-time error.

try, raise and asm

try … except … end, try … finally … end and raise are described on Exceptions and memory. An asm … end block is a statement that holds assembly language, described on Assembler.

Empty statement

A statement may be empty: if Done then ;, repeat until Done;, begin end. An unintended empty statement after a stray semicolon, as in for I := 1 to 10 do;, is a common mistake that makes the loop run an empty body.

.PAS File Format – Statements