if conditional judgment

Use if .. then or if .. then .. else to run corresponding code when the condition is true. Unlike C-style languages: the conditional expression in Pascal does not need parentheses.

var
  A: Integer;
  B: boolean;
begin
  // Only one statement after condition, no begin end required
  if A > 0 then
    DoSomething;

  // Multiple statements after condition, must wrap with begin end
  if A > 0 then
  begin
    DoSomething;
    AndDoSomethingMore;
  end;

  // Single-line if-else structure
  if A > 10 then
    DoSomething
  else
    DoSomethingElse;

  // Identical logic to above: store comparison result into boolean variable first
  B := A > 10;
  if B then
    DoSomething
  else
    DoSomethingElse;
end;Code language: JavaScript (javascript)

else Matching Rule

else binds to the nearest unmatched if. The code below works as expected:

if A <> 0 then
  if B <> 0 then
    AIsNonzeroAndBToo
  else
    AIsNonzeroButBIsZero;Code language: HTML, XML (xml)

The else here belongs to the inner if B <> 0.

Nested if without block wrapping is syntactically valid but hard to read. It’s recommended to wrap inner nested logic with begin … end for clear logical boundaries; even with messy indentation, readers can easily distinguish scopes and avoid bugs when adding/removing branches.

Optimized standard writing style:

if A <> 0 then
begin
  if B <> 0 then
    AIsNonzeroAndBToo
  else
    AIsNonzeroButBIsZero;
end;Code language: HTML, XML (xml)

• No parentheses around if conditions (mandatory in C/C++/Java, opposite in Pascal);
• Omit begin end if only one line after then; mandatory for multiple lines;
• else matches the nearest inner if; always use blocks for nested conditions to eliminate ambiguity;
• Comparison expressions (e.g. A>10) can be directly assigned to boolean variables.

Below is a runnable full example: score grading system

Logic rules:

• ≥90 → A
• ≥80 and <90 → B
• ≥60 and <80 → C
• <60 → D

{$ifdef FPC} {$mode objfpc} {$H+} {$endif}
{$codepage utf8}
program ScoreLevel;

var
  score: Integer;
begin
  Write('Please enter exam score: ');
  ReadLn(score);

  if score >= 90 then
    Writeln('Grade: A')
  else if score >= 80 then
    Writeln('Grade: B')
  else if score >= 60 then
    Writeln('Grade: C')
  else
    Writeln('Grade: D');

  ReadLn;
end.Code language: PHP (php)

Compile and run

Please enter exam score: 96
Grade: A

The program prompts for score input and outputs corresponding grade.

Non-English text may show garbled characters, add this line: {$codepage utf8}

We can also wrap grade calculation into a function.

{$ifdef FPC} {$mode objfpc} {$H+} {$endif}
{$codepage utf8}
program ScoreLevelFunc;

function GetLevel(s: Integer): string;
begin
  if s >= 90 then
    Result := 'A'
  else if s >= 80 then
    Result := 'B'
  else if s >= 60 then
    Result := 'C'
  else
    Result := 'D';
end;

var
  score: Integer;
begin
  Write('Your score: ');
  ReadLn(score);
  Writeln('Your grade: ', GetLevel(score));
  ReadLn;
end.Code language: PHP (php)

if conditional judgment