LOST please help with if/else elseif and unless I can't seem to define



I seem to have somehow luckboxed my way to the review part of this lesson and I honestly don't understand the effective use of if or else or elseif or unless. I don't know how these functions differ exactly and when each one should be correctly applied.

Replace this line with your code.


Here is my code:

if a<b
  print "a is less than b!"
elsif b<a
  print "b is less than a"
  print "b is equal to a"

The lesson was correct but only because I copied their example I don't understand because we first said a is less than b then used elseif to say the opposite then else to say that they are equal. I guess I am confused because there is no absolute definition what role does if else and elseif play in defining these comparisons?? Could we say the same thing only swaping else where elseif is? Or else where if is?? Does my question make sense??


if-elseif-else are the building blocks of any modern program. They help us take decisions.

Consider a real-world decision. You are a student, and you only need to carry your Maths book if your maths teacher is coming to give a lecture. You make a mental note like this:

if maths_teacher == true
    print "bring maths book to school"
    print "no need to carry maths book!"

but, you need to carry your geometry book in case the geometry teacher comes in place of maths teacher, so you write:

Elsif refers to that branch of code that is checked only if the previous condition failed.

if maths_teacher== true
    print "bring maths book to school"
elsif geometry_teacher == true
    print "bring geometry book to school"
    print "no need to carry maths/geomtery book!"

remember that here the elsif branch is only checked if the if condition failed. When you are printing "bring geometry book to school" you are certain that the boolean geometry_teacher was true and maths_teacher was false. Because maths_teacher boolean was false, the elsif condition was checked and because geometry_teacher boolean was true, the elsif part's print statement got executed.

Hope that helps! :smiley:


Hey @ihabacode,
well, your question is a bit weird.

EDIT: Oh well, @gaurangtandon was a little bit faster than me :stuck_out_tongue:
Nevermind, here is my solution:

Here a little explanations - in case you don't know how if-else-constructs work:

/* Here you got two so-called "hard-coded" variables.
Variables can be - as their name says - variable,
so their value can change */
a = 20 
b = 22

/* Here starts your if-else construct */
if a < b 

/* if the value of a is smaller than the value of b, 
this part of the if-elsif-else-construct gets executed 
- like in this case */

    print "a is less than b!"

elsif b<a

/* If the value of b is smaller than the value of a,
this part of the if-elsif-else-construct gets executed,
- that's not the case */

    print "b is less than a!"


/* Otherwise, if none of the both upper cases apply,
this part of the if-elsif-else-construct gets executes.
- in this case, this would happen, if both variables would 
have the same value */

    print "b is equal to a!"

/* And here is the very end of your if-elsif-else */

Hope that will help you understanding. :slight_smile:


Your answer made up for what I missed. Together I hope we've solved OP's problem :smiley: