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Ruby Ruby Foundations Loops Creating Loops

Posted by M Fen
M Fen
9,858 Points

Why does the = sign need to be on the += incriminator?

If you take the = sign of the += it runs forever. Why do you need the = sign? Just curious if anyone knows. 

i = 0
string = "hello world"

while i <= 10
    string = "hello world #{i}"
    puts "i is now #{i}"

i += 1

end
Andrew Gay
Andrew Gay
20,893 Points

The = character in most programming languages is known the assignment operator.

So i + 1 will output whatever i + 1 is (In this case you assigned i to 0, so 0 + 1 = 1) but not actually assign that output to any variable (such as i). Instead, the code would continue through the loop outputting 1 infinity but again not actually assigning that value to i and as i remains 0 and is always less than 10 the loop would continue.

Edit: Had to edit this a few time in attempt to make it more clear but hope this helped! Also thank Kyle Daugherty for the verification!

Kyle Daugherty
Kyle Daugherty
16,441 Points
Kyle Daugherty
Kyle Daugherty
16,441 Points

Andrew, you are spot on!

Cheers!

1 Answer

Maciej Czuchnowski
Maciej Czuchnowski
36,441 Points
Maciej Czuchnowski
Maciej Czuchnowski
36,441 Points

Think of it this way:

Numbers, such as 1, 2 and 3, are constants that always have fixed values - 1, 2 and 3 accordingly (think "variables with fixed values and names that are exactly the same as values" - the constant named 2 has the value 2). So if you do this:

1 + 2

You get the result 3, but you did not change the value of 1 or 2 at any point - if you check the value of 2 after this operation, it will still be 2. So similarly, if you create a variable x and give it a value 5, and then do this:

x + 2

You will get a result of 7, but you did not modify the value of x. It is still 5, just like 2 remained 2 in the previous example.

The difference between constants and variables becomes noticeable when you try to modify the values. And to modify the values, you use the = symbol (it doesn't work the exact same way it does in simple math). This symbol modifies the value.

If you try to modify the value of x, no problem. This will change the value of x to anything you want:

irb :002 > x = 5
 => 5 
irb :003 > x = 7
 => 7

But if you try to change the value of 2, it will not work and will give you an error.

irb :001 > 2 = 3
SyntaxError: (irb):1: syntax error, unexpected '=', expecting end-of-input
2 = 3
   ^

Because 2 has a constant value of 2 and cannot be changed.

This:

i += 1

Is a shorthand for this:

i = i + 1

And reads "take the current value of i, add 1 to it, and make the result the new value of i". The right-hand side is always evaluated first and the result is then assigned to the variable given on the left-hand side.