Location of an element where index is same as the value

In a sorted integer array,

find an index, for which the
value is same as the index, i.e. a[i] is same as i.

For e.g. in a = {-2,0,2,3}
a[2] is 2, so the answer is 2.

In {1,2,5,7}, there is no such index.

My answer is on the lines of binary-search,
but would also like to see other answers.