Pascal Programming

Covers Pascal — designed by Niklaus Wirth explicitly to teach structured programming through strong static typing and clear, readable syntax. Delphi Programming uses Object Pascal, a direct object-oriented descendant of the language covered here.

Strong static typing

program TypeExample;
var
  age: Integer;
  name: String;
  price: Real;
begin
  age := 30;
  name := 'Ada';
  price := 19.99;
  { age := name;  ← compile error: type mismatch, caught before running }
end.

Every variable has a fixed, declared type, checked at compile time — Pascal was deliberately designed to make type errors (assigning a string to an integer variable, for instance) impossible to compile, reflecting Wirth's broader philosophy that a language should guide programmers toward correct code by construction.

Structured programming constructs

procedure PrintFactorial(n: Integer);
var
  i, result: Integer;
begin
  result := 1;
  for i := 1 to n do
    result := result * i;
  WriteLn('Factorial: ', result);
end;

begin
  PrintFactorial(5);
end.

Pascal was one of the languages that popularized structured programming: begin/end blocks, if/then/else, for/while/repeat loops, and named procedures/functions, explicitly without goto-driven control flow (though Pascal does technically support goto, its use is discouraged and rare in idiomatic code) — a deliberate rejection of the unstructured, jump-heavy style common before it.

Units (modularity)

unit MathUtils;

interface
  function Square(x: Integer): Integer;

implementation
  function Square(x: Integer): Integer;
  begin
    Square := x * x;
  end;
end.

A unit separates a module's public interface from its implementation — conceptually similar to a header/source file split in C, but built into the language rather than handled by a preprocessor.

Common pitfalls

• Off-by-one errors in for loops — Pascal's for i := 1 to n do is inclusive of both ends; forgetting this compared to a half-open-range language is a common source of boundary bugs.
• Confusing = (comparison) and := (assignment) — Pascal uses := for assignment and = strictly for comparison, unlike C-family languages where = is assignment; muscle memory from another language can cause mistakes here.
• Fixed-size string handling in older dialects — standard Pascal's original string type had compile-time fixed length; modern dialects (Free Pascal, Delphi's Object Pascal) use dynamically-sized strings, so check which dialect a specific codebase targets.
• Treating all "Pascal" dialects as identical — standard Pascal, Free Pascal (Object Pascal-compatible), Turbo Pascal, and Delphi's Object Pascal differ meaningfully; verify which dialect a given piece of code or documentation assumes.

Learn more

• Free Pascal documentation
• Delphi Programming for the object-oriented Object Pascal dialect built on this foundation.