−1In mathematics, −1 is the additive inverse of 1, that is, the number that when added to 1 gives the additive identity element, 0. It is the negative integer greater than negative two (−2) and less than 0.
Negative one bears relation to Euler's identity since ''e''}} = −1.
In software development, −1 is a common initial value for integers and is also used to show that a variable contains no useful information.
In programming languages, −1 can be used to index the last (or 2nd last) item of an array, depending on whether 0 or 1 represents the first item.
Negative one has some similar but slightly different properties to positive one. Provided by Wikipedia