ListProj

program ListProj;

const MYSTERIOUS_NUMBER = 57978;
// Эта константа вводится для возможности добавления в список полноправного числа 0

var
  count, userCount, elementIndex : byte;
  list : array[0..5] of integer;
  element, elementOld, i, ii, iii : integer;
  answer : string;
  wasFound : boolean;

function isAMysteriousNumber(number : integer) : boolean;
begin
  if (number = MYSTERIOUS_NUMBER) then
  begin
    isAMysteriousNumber := true;
  end else
  begin
    isAMysteriousNumber := false;
  end;
end;

function thereIsAPlaceOnTheRightBefore(index : integer) : boolean;
var
  cycleVar : integer;
begin
  for cycleVar := index to 5 do
  begin
    if (list[cycleVar] = MYSTERIOUS_NUMBER) then
    begin
      thereIsAPlaceOnTheRightBefore := true;
      break;
    end;
    if (cycleVar = 5) then
    begin
      thereIsAPlaceOnTheRightBefore := false;
      break;
    end;
  end;
end;

function Push(element, elementIndex : integer) : integer;
 begin
   if (count <= 5) then
   begin
     List[elementIndex] := element;
     count += 1;
   end else
   begin
   if (count > 5) then
     writeln;
     writeln('!!!!!!!!!!ERROR: the List is overloaded!!!!!!!!!!');
     writeln;
   end;
 end;

function Pop(elementIndex : integer) : integer;
begin
  if (count > 0) then
  begin
    if (List[elementIndex] <> 0) then
    begin
      List[elementIndex] := MYSTERIOUS_NUMBER;
      count -= 1;
    end else
    begin
      writeln;
      writeln('!!!!!!!!!!ERROR: Element index is empty!!!!!!!!!!');
    end;
  end else
  begin
    writeln;
    writeln('!!!!!!!!!!ERROR: List is empty!!!!!!!!!!');
    writeln;
  end;
end;

procedure PushBefore();
var
  endOfCycle : boolean;
  j : integer;
begin
  write('Enter the element BEFORE which you want to add a new element: ');
  readln(elementOld);
  write('Enter the new element: ');
  readln(element);
  wasFound := false;
  if (count > 0) then
  begin
    for i := 0 to 5 do
    begin
      if (list[i] = elementOld) then
      begin
        if thereIsAPlaceOnTheRightBefore(i - 1) then
        begin
          if (list[i - 1] = MYSTERIOUS_NUMBER) then
          begin
            list[i - 1] := element;
            count += 1;
          end else
          begin
            repeat
            for ii := 1 to 5 do                   // 0 7 6 4 0 0
            begin
              if (list[i + ii] = MYSTERIOUS_NUMBER) then
              begin
                list[i + ii] := list[i + ii - 1];
                list[i + ii - 1] := MYSTERIOUS_NUMBER;
                if list[i] = MYSTERIOUS_NUMBER then
                begin
                  list[i] := element;
                  count += 1;
                  endOfCycle := true;
                  break;
                end;
                break;
              end;
            end;
            until endOfCycle;
          end;
        end else
        begin
          writeln;
          writeln('!!!!!!!!!!ERROR: The element ', list[i], ' is the first element!!!!!!!!!!');
          writeln;
        end;
        wasFound := true;
        break;
      end;
    end;
    if (not wasFound) then
    begin
      writeln();
      writeln('!!!!!!!!!!ERROR: The element ', elementOld, ' was not founded!!!!!!!!!!');
      writeln();
    end;
  end else
  begin
    writeln('!!!!!!!!!!ERROR: List is empty!!!!!!!!!!');
  end;
end;

procedure PushAfter();
var
  endOfCycle : boolean;
begin
  write('Enter the element AFTER which you want to add a new element: ');
  readln(elementOld);
  write('Enter the new element: ');
  readln(element);
  wasFound := false;
  if (count > 0) then
  begin
    for i := 0 to 5 do
    begin
      if (list[i] = elementOld) then
      begin
        if thereIsAPlaceOnTheRightBefore(i) then
        begin
          if (list[i + 1] = MYSTERIOUS_NUMBER) then
          begin
            writeln('i');
            list[i + 1] := element;
            count += 1;
          end else
          begin
            repeat
            for ii := 1 to 5 do                   // 0 7 6 4 3 0
            begin
              if (list[i + 1 + ii] = MYSTERIOUS_NUMBER) then
              begin
                list[i + 1 + ii] := list[i + 1 + ii - 1];
                list[i + 1 + ii - 1] := MYSTERIOUS_NUMBER;
                if list[i + 1] = MYSTERIOUS_NUMBER then
                begin
                  list[i + 1] := element;
                  count += 1;
                  endOfCycle := true;
                  break;
                end;
              end;
            end;
            until endOfCycle;
          end;
        end else
          begin
            writeln;
            writeln('!!!!!!!!!!ERROR: The element ', list[i], ' is the last element or list is overloaded!!!!!!!!!!');
            writeln;
          end;
        wasFound := true;
        break;
      end;
    end;
    if (not wasFound) then
    begin
      writeln();
      writeln('!!!!!!!!!!ERROR: The element ', elementOld, ' was not founded!!!!!!!!!!');
      writeln();
    end;
  end else
  begin
    writeln('!!!!!!!!!!ERROR: List is empty!!!!!!!!!!');
  end;
end;

begin
  count := 0;
  for i := 0 to 5 do list[i] := MYSTERIOUS_NUMBER;
  repeat
    begin
      write('Current List:                     [ ');
      for i := 0 to 5 do if isAMysteriousNumber(list[i]) then write(' - ') else write(' ', list[i], ' ');
      writeln(']');
      writeln('1. Add element to List');
      writeln('2. Remove element from List');
      writeln('3. Add element before...');
      writeln('4. Add element after...');
      writeln('5. Close the programm');
      readln(answer);
      writeln();

      case answer of
      '1':
        begin
          write('Enter element index to add(first element index = 0): ');
          readln(elementIndex);
          write('Enter element: ');
          readln(element);
          if ((0 <= elementIndex) AND (elementIndex <= 5)) then Push(element, elementIndex) else writeln('error :0');
        end;
      '2':
        begin
          write('Enter element index to remove(first element index = 0): ');
          readln(elementIndex);
          if ((-1 < elementIndex) AND (elementIndex < 6)) then
          begin
            write('Removing element from List - ');
            if (List[elementIndex] = MYSTERIOUS_NUMBER) then
            begin
              writeln('NaN');
            end else writeln(List[elementIndex]);
            Pop(elementIndex);
          end else
          begin
            writeln;
            writeln('element index must be from 0 to 5!');
          end;
        end;
      '3': PushBefore();
      '4': PushAfter();
      end;

    end
  until answer = ('5');
end.