Note: There are no such thing as negative years.
15. A double function named Distance2D() that takes four double parameters named x1, y1, x2 and y2
respectively. It returns the distance between the points (x1,y1) and (x2,y2) where x1 is equal to x1, y1 is
equal to y1, x2 is equal to x2 and y2 is equal to y2;
Note: Include the cmath library to calculate the square root.
16. A void function named Invite() that takes seven string parameters named name1, theme, name2,
place, weekday, time and email respectively. It displays the message:
Dear (name1),
You are invited to a (theme) party hosted by (name2)!
It's going to be at (place) on (weekday).
Please make sure to show up at (time).
RSVP at (email).
in the exact same format with a line before and after it where (name1) is the value of name1, (theme)
is the value of theme, (name2) is the value of name2, (place) is the value of place, (weekday) is the
value of weekday, (time) is the value of time, and (email) is the value of email.
17. A void function named NumberSwap() that takes two double reference parameters named x and y
respectively. It swaps the values of x and y.
[You cannot declare any additional variables.]
18. A void function named Permutation() that takes four int parameters named a, b, c and d respectively.
It displays all arrangements of the parameters. For each arrangement the elements must be separated by
a comma and the arrangement must be enclosed in parentheses. Furthermore, four arrangements must be
on each line with a space between each arrangement.
[You can only use a single cout statement.]
