Objective

Write a function that returns how many days the month month of the year year has, and -1 when month is not a month number.

Steps

• month is a month number: 1 is January, 12 is December. year is the calendar year that month falls in.
• January, March, May, July, August, October and December have 31 days.
• April, June, September and November have 30 days.
• February has 29 days in a leap year and 28 days otherwise, which is the only place year is used.
• A year is a leap year when it divides by 4, except that a year dividing by 100 is not one, unless it also divides by 400. 2024 is a leap year, 1900 is not, 2000 is.
• Outside February the year is irrelevant. April has 30 days in 2000 and 30 days in 2001.
• Return -1 when month is below 1 or above 12. That covers 0, 13 and every negative value.

Objective

Write a function that returns how many days the month month of the year year has, and -1 when month is not a month number.

Steps

• month is a month number: 1 is January, 12 is December. year is the calendar year that month falls in.
• January, March, May, July, August, October and December have 31 days.
• April, June, September and November have 30 days.
• February has 29 days in a leap year and 28 days otherwise, which is the only place year is used.
• A year is a leap year when it divides by 4, except that a year dividing by 100 is not one, unless it also divides by 400. 2024 is a leap year, 1900 is not, 2000 is.
• Outside February the year is irrelevant. April has 30 days in 2000 and 30 days in 2001.
• Return -1 when month is below 1 or above 12. That covers 0, 13 and every negative value.