  Let $X,Y$ be $(n-1)$-connected finite pointed CW-complexes of dimension at
most $n+2$, $n\geq 3$. In this paper we give elementary proofs of the abelian
group structure of $[X,Y]$ of homotopy classes of based maps from $X$ to $Y$,
which was due to Baues and Schmidt. Furthermore, we determine the explicit
generators associated to $[X,Y]$. As an application, we compute certain
(sub)groups of self-homotopy equivalences of certain Chang complexes.
