Using a Boolean Chain

function LeapYear(const year : integer) : boolean;
begin
  result := (year mod 400 = 0) or ((year mod 4 = 0) and (year mod 100 <> 0));
end;

The mod operator returns the remainder of integer division — equivalent to % in C. year mod 4 = 0 is true when year is evenly divisible by 4.

and and or are Pascal's boolean operators, written as keywords rather than symbols. && in C maps to and; || in C maps to or.

<> is Pascal's not-equal operator, equivalent to != in C.

and binds more tightly than or, so the inner parentheses around the and subexpression are not strictly required — but they are included here for clarity. Both operators also short-circuit: when the left operand of or is true, the right operand is not evaluated; when the left operand of and is false, the right operand is not evaluated.

The result variable is implicitly declared in every Pascal function and holds the return value. Assigning to result without calling exit allows the function to reach its final end and return normally.