12. If $\sin \alpha \cdot \cos \beta=1$, then $\cos \alpha \cdot \sin \beta=$
12.0.

From $\sin \alpha \cdot \cos \beta=1$ and the boundedness of sine and cosine functions, we know that $\sin \alpha=\cos \beta=1$ or $\sin \alpha=\cos \beta=-1$. Therefore, $\cos \alpha=\sin \beta=0$, which means $\cos \alpha \cdot \sin \beta=0$.