Suppose that we are to trace the algorithm that counts the number of $O$ s in the bit string $0110$

$($algorithm is provided below$).$ After the second pass of the "for" loop $($that is$,$ after we execute

the $i=2$ step of the "for" loop$),$ what is the value of "counter?"

Input: A bit string $a_1,a_2,$dots,$a_n$ and a positive integer $n.$

Initialize: counter:$=0.$

For i starting from $1$ up through $n.$

If $a_i=0$ then update counter :$=$ counter $+1.($This increases the value of counter by $1.)$

Output: counter.

$0$

$1$

$2$

$3$