Write a function count_evens(a, b) that returns how many even integers lie between a and b, including both ends. Remember that 0 is even and negative numbers can be even too.
Examples
Input: a = 1, b = 10
Output: 5
Explanation: 2, 4, 6, 8, 10
Input: a = -3, b = 3
Output: 3
Explanation: -2, 0, 2
Constraints
-10**5 <= a <= b <= 10**5
Goals
- Loop over an inclusive range of integers
- Count how many items satisfy a condition