[c-prog] scanf and &

[ruhatadiyaman]

as i said i started C from Deitel and i wrote some examples from book.
there was a example about function scanf. 
i write it as scanf("%d", var);  and then compiled. but it runs
windows gives error, and stop the program.
then i look in web so i see &. 
when i write the code as scanf("%d", &var);
and it works
my question; why it needs & and why is there not & in the book?
best regards