Multiple if then statements

I want to make this so that it will send the respective rednet broadcasts, and that works. I also want it to say "Invalid Floor!" for any number other and 1,2, and 3.

rednet.open("back")
while true do
term.clear()
term.setCursorPos(1, 1)
print("Enter Desired Floor #:")
input = read()
if input == "1" then
rednet.broadcast("1")
if input == "2" then
rednet.broadcast("2")
if input == "3" then
rednet.broadcast("3")
else print("Invalid Floor!")
  sleep(3)
end
end

Right now it just gives me a bunch of errors about expecting end in places to close the while true statement.
How can I make this work?

You should be using elseif instead of if for options 2 and 3.

Lua syntax for the a simple if/then control structure is this:

if(condition)then
    doSomething()
end

You code lacks the "end" keyword to close each if/then structure. This is why you get the errors.

[EDITED]
However, it is correct to do as lyqyd suggests, so that you have if-then / elseif-then / elseif-then / else. Otherwise your else block at the end will also catch the cases where input=1 and input=2, which is probably not what you want.

Using elseif instead of more if blocks also allows the final else to behave as expected.

Good point. With the original example an input value of 1 would trigger both the first if/then AND the else in the last if/then/else. Doh! My bad. Edited my first post to reflect this.