C$++$

$(2)$ Write a program that reads in a $2-$dimensional array $($matrix$)$ with $n$ rows and $m$ columns where $n$ and $m$ are user$-$given and for each column it computes its average.

E$.$g$.,$ for the matrix

$123$

$56$

$383$

the average of $1^{st}$ column is $3\mathrm{.}333333,$ of $2^{nd}$ column is $5\mathrm{.}0,$ and of $3^{rd}$ column is $4\mathrm{.}0.$