[PASCAL] Binary Search

[CouldnoT]

Binary Search

 

A binary search first compares the search item to an item at the middle of the list. If there is not a match, the code determines which half of the list to carry out the next search using the same method. This iterative or recursive process is repeated until the search item is found or it is shown to be absent.

 

 

This is a demonstration for the binary search :

 

program BinarySearchDemo;
const
  UPPER_BOUND = 16;
  Nums : array[1 .. UPPER_BOUND] of integer =  (61, 87, 154, 170, 275,
           426, 503, 509, 512, 612, 653, 677, 703, 765, 897, 908);
var
  Num : integer;

procedure BinarySearch(SearchNum : integer);
var
  Found, Failed: Boolean;
  Last, First, MidPoint: integer;
begin
  Found := False;
  Failed:= False;
  Last := UPPER_BOUND;
  First := 1;
  repeat
    Midpoint := (First + Last) DIV 2;
    if Nums[MidPoint] = SearchNum then
      begin
        Found := True;
        writeln('Found at position ' ,MidPoint);
      end
    else if (First > Last) then
      Failed := true;
    else if Nums[MidPoint] < SearchNum then
      First := MidPoint + 1;
    else
      Last := MidPoint - 1;
  until Found or Failed;
  if Failed then
    writeln('Not found.');
end;

begin
  writeln('Enter the number to search for: ');
  readln(Num);
  BinarySearch(Num);
  readln;
end.

 

 

Edited August 17, 2020 by CouldnoT

[CouldnoT]

Edited October 21, 2020 by CouldnoT