Which of the following form(s) the virtual and erect image for all positions of object?

For a lens, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f} \Rightarrow \frac{1}{v}=\frac{1}{f}+\frac{1}{u}$

For a concave lens, $f$ and $u$ are negative, i.e., $v$ will always be negative and image will always be virtual.

For a mirror, $\frac{1}{v}+\frac{1}{u}=\frac{1}{f} \Rightarrow \frac{1}{v}=\frac{1}{f}-\frac{1}{u}$

Here, $f$ is positive and $u$ is negative for a convex mirror. Therefore, $v$ is always positive and image is always virtual.