wiki/articles/pascal.md

Pascal

Pascal is a procedural programming language created by Niklaus Wirth in 1970.

Pascal was a popular choice for microcomputers in the 70's and 80's, even more popular than C initially (C was still quite an UNIX-only language) due to its simple design, which allowed fast simple single-pass compilers.

In its "vanilla" form, Pascal is not any more complex than C, aside from having features that C doesn't have, such as range types and nested procedures.

Compilers

• FPC (Free Pascal Compiler): currently the most popular Pascal compiler with wide support for different OSes and architectures, libre software.
• Turbo Pascal: old compiler for DOS systems, proprietary.
• Delphi: proprietary, adds OOP bloat and exception handling.

Notes

Returning values from functions

{ The "classical" way, assigning the return value to the function name }
function Square(n: integer): integer;
begin
    Square := n * n; 
end;

{ Object Pascal and Delphi, assigning to special `Result` variable }
{ Enable with `-S2` in FPC }
function Square(n: integer): integer;
begin
    Result := n * n; 
end;

{ Return statement like }
function Square(n: integer): integer;
begin
    Exit(n * n);
end;

Examples

Hello world

program HelloWorld;

begin
    WriteLn('Hello, World!');
end.

And then compile:

fpc hellopascal.pas

Factorial

{
Calculate a factorial on multiple languages: Pascal version
Compile with: fpc -O3 -S2 fact.pas
}
program Factorials;

{ qword = 64 bit unsigned type }
function FactorialRec(n, acc: qword): qword;
begin
    if n <= 0 then
        Result := acc
    else
        Result := FactorialRec(n - 1, acc * n);
end;

function FactorialIter(n: qword): qword;
begin
    Result := 1;
    while n > 0 do
    begin
        { The usage of C-like arithmetic assignment operators is possible with -Sc: }
        { Result *= n; }
        Result := Result * n;
        Dec(n); { equivalent to C's `--` operator }
    end;
end;

var
    n: qword;
    values: array of qword = (14, 5, 2, 10, 1, 18, 4);
begin
    Assert((FactorialIter(0) = 1) and (FactorialRec(0, 1) = 1));
    for n in values do
    begin
        WriteLn('Factorial of ', n, ' = ',  FactorialRec(n, 1));
    end;
end.

Resources

• Free Pascal Wiki
• Basic Pascal Tutorial
• Why Pascal is Not My Favorite Programming Language by Brian Kernighan, mostly of historic interest as almost all of the flaws described in the article has been fixed by modern Pascal compilers. https://www.lysator.liu.se/c/bwk-on-pascal.html

See also

• Oberon