var a := [1, 2, 3, 4];
var b := [5, 6, 7, 8, 1];
var c: TArray<integer>;
SetLength(c, Max(Length(a), Length(b)));
for var i := 0 to High(c) do
if (i < Length(a)) and (i < Length(b)) then
c[i] := a[i] + b[i]
else if i < Length(a) then
c[i] := a[i]
else
c[i] := b[i];