C++ exercise 1.9 - C++ Primer 4th edition 2005

C++ Primer Fourth Edition 2005
ISBN-13: 978-0-201-72148-5
ISBN:10: 0-201-72148-1
Page 17.
Exercise Section 1.4.2
Exercise 1.9: What does the following for loop do? What is the final value of sum?

int sum = 0;
for(int i = -100; i <= 100; ++i)
    sum += i;