$4.$ Given a year, write a c program to check if it is a leap year or not. A leap year is a year that has $366$ days, instead of $365$ days. It has one day extra in the month of February. Leap years occur once in $4$ years, so any year that is completely divisible by four should be a leap year. But this is not always true. If a year is divisible by a hundred, it will be a leap year only if it is also divisible by four hundred.