What number is next 1. 2 0 3 -1?

The sequence appears to alternate between adding and subtracting values. Starting from 1: add 1 to get 2, then subtract 2 to get 0, add 3 to get 3, and subtract 4 to get -1. Following this pattern, the next step would be to add 5, which results in 4. Therefore, the next number is 4.