[c] algorithm problem

Given two sorted arrays of integers of size n,
i.e. a[n] and b[n], please find all pairs <value_1, value_2>

so that value from a[n], value_2 from b[n]
and value_1+ value_2=Constant, e.g. Constant=100.
and n<100.

Constraint: O(n) time, O(1) extra space

i cant think of any way of not using nested loop
pls help me

Start with some paper, and some simple examples of short sorted arrays.

My suggestion - start at opposite ends of each array.