What is a reference variable? What is its use?

What is the difference between 56L and 56?

Determine which of the following are valid constant? And specify their type.
(i) 0.5
(ii) ‘Name’
(iii) ‘\t’
(iv) 27,822

What will be the result of following if num=6 initially.
(a) cout << num;
(b) cout << (num == 5);

Which of the following two statements are valid? Why? Also write their result.
int a;
(i) int a; a = 3,014;
(ii) int a; a=(3,014);