Sum of Alternating Integers

What is the value of $1+\textrm{-}2+3+\textrm{-}4+\cdots+99+\textrm{-}100$ (alternating signs for each term)?
Source: NCTM Mathematics Teacher 2006

SOLUTION
The sum consists of $50$ additions of a positive and a negative integer each resulting in $\textrm{-}1$
$1+\textrm{-}2=\textrm{-}1$
$3+\textrm{-}4=\textrm{-}1$
$\cdots$
$97+\textrm{-}98=\textrm{-}1$
$99+\textrm{-}100=\textrm{-}1$
$1+\textrm{-}2+3+\textrm{-}4+\cdots+99+\textrm{-}100=\textrm{-}50$

Answer: $\textrm{-}50$