What is a null statement and compound statement?

What is selection statement? write it's types?

Correct the following code sigment:
if (x = 1)
p = 100;
else
p = 10;

What will be the output of the following code:
int year;
cin >> year;
if (year % 100 == 0)
if ( year % 400 == 0)
cout << "Leap";
else
cout << "Not Leap year";
If the input given is
(i) 2000
(ii) 2003
(iii) 2010?

What is the output of the following code?
for (int i = 2; i < = 10 ; i + = 2)
cout << i;