First of all, we must find out which months are big months, which months are small months and the number of days in February. There is a formula: one, three, five, seven, eight, ten, wax, 3 1 day is never bad; Secondly, leap year judgment. A year divisible by 4 is a leap year (whole hundred is divisible by 400). There are 29 days in February in leap year and only 28 days in normal year. Four, six, nine, eleven, these four months are abortion, only 30 days; Secondly, the calculation method of the intermediate days is whether the head is counted but not the tail, or whether the tail is counted and not the head.

For example, how many days passed from 20 1 1 to March 5?

First of all, we should judge that 20 1 1 is a normal year, and February has 28 days.

There are 7 days in February and 5 days in March (this is the way to count tails instead of heads), * * * has passed 12 days.