Як виконуется цикл з передумовою?​

А)uses crt;
const n=20;
var a:array[1..n] of integer;
i,s,k:integer;
begin
randomize;
s:=0;
k:=0;
for i:=1 to n do
begin
a[i]:=random(100)-50;
writeln(a[i]);
end;
writeln;
for i:=1 to n do
begin
if (a[i] mod 2=0) and (i mod 2 =0) and (a[i]<0)
then
begin
inc(k);
s:=s+a[i];
end;
end;
writeln(s);
writeln(k);
end.

б)uses crt;
const n=20;
var a:array[1..n] of integer;
i,s,k:integer;
begin
randomize;
s:=0;
k:=0;
for i:=1 to n do
begin
a[i]:=random(100)-50;
writeln(a[i]);
end;
writeln;
for i:=1 to n do
begin
if (a[i]mod 3=0) and (a[i] mod 5<>0) then
begin
s:=s+a[i];
inc(k);
end;
end;
writeln(s);
writeln(k);
end.

в)uses crt;
const n=20;
var a:array[1..n] of integer;
i,s,k:integer;
begin
randomize;
s:=0;
k:=0;
for i:=1 to n do
begin
a[i]:=random(100)-50;
writeln(a[i]);
end;
writeln;
for i:=1 to n do
begin
if (abs(a[i]))>(i-2)
then
begin
inc(k);
s:=s+a[i];
end;
end;
writeln(s);
writeln(k);
end.

Program Ulitka;
Var SunnyDay: Array [1..30] Of Boolean;
a, b, c, i: Integer;
Begin
WriteLn('a = ');
ReadLn(a);
WriteLn('b = ');
ReadLn(b);
b := b * 100;
Randomize;
For i := 1 To 30 Do
Begin
If Random(2) = 1 Then
SunnyDay[i] := True
Else SunnyDay[i] := False;
End;
For i := 1 To 30 Do Begin
If SunnyDay[i] = True Then
Begin
a := a + 2;
If a > b Then
a := b;
End
Else
Begin
a := a - 1;
If a < 0 Then
a := 0;
End;
End;
WriteLn('Дни месяца были таковы:');
For i := 1 To 30 Do Begin
If SunnyDay[i] = True Then
WriteLn(i, '. Солнечный')
Else
WriteLn(i, '. Пасмурный') End; WriteLn('К концу 30 дня местоположение улитки равно ', a, ' см над землей');
ReadLn;
End.