Syntax errors are often the easiest problems to find and fix.

Suppose that we get this error when loading the list of pets.

We see SyntaxError in PetsController#index.

We get a file name and a line number, and we see syntax error, unexpected '>'.

The error points us directly to the file and line number where the problem is,

line one of app/models/pet.rb.

In this case,

we even get a hint as to the nature of the problem, unexpected greater than sign.

Let's do a web search to figure out what went wrong.

This line is the start of a class definition, so we'll search for Ruby class

definition.

Skimming the results, we see one that talks about using a less than symbol.

That looks interesting, so let's check that out.

If we scroll down, we see a section on class inheritance.

That's relevant to us because our model class inherits from Application Record.

And in their sample code, it looks like they're using a less than symbol to

indicate a subclass, not a greater than symbol.

So the error is that we're supposed to use a less than symbol to indicate that Pet is

a subclass of ActiveRecord Base, not a greater than symbol.

Let's try changing that, save our work, and reload our page.

It looks like everything works again.

Let's look at another common mistake in code.

Sometimes Ruby will indicate the error occurred on one line but

the real problem is elsewhere in the file.

Suppose we get this error when loading the pets index.

Syntax error in PetsController#index.

It indicates a problem on the pets_controller.rb file line 56.

Let's open that file and line number and see if we can figure out what's going on.

So app/controllers/pets_controller, and we'll scroll down to line 56.

We don't really see a problem here, line 56 is just the end of the file.

But if we scroll higher in the file, suppose we see this.

See something odd there?

There's no end keyword at the end of the new definition.

So Ruby thinks that all the remaining code in the file is part of the new method.

An error doesn't get reported until the end of the file

when Ruby fails to find the expected number of end keywords.

So let's add that end keyword back in, save and reload and our problem is fixed.

So while Ruby and Rails try to guide you directly to the line with the problem,

sometimes that isn't possible.

If this happens, be prepared to widen your search a little bit.

There's one more common issue I'd like to show you.

Sometimes typos in your code cause syntax errors and sometimes they cause undefined

variable or undefined method errors, but you fix them in much the same way.

Suppose we're trying to load the show view for an individual pet,

but we're getting this error.

It says, NameError in Pets#show and it's showing an error in

the show.html.erb template, undefined local variable or method pet.

Here's a potentially helpful error message.

Did you mean @pet, the instance variable?

The problem is that we forgot the at symbol character at the start of the pet

instance variable name.

So Ruby thinks we're trying to access a local variable named pet

rather than an instance variable named @pet.

So if we open up app/views/pets/show.html.erb,

and there on line five, you see the misnamed variable.

If we add an at symbol, save our work, and reload,

everything works.

Thus far, we've focused on fixing error messages, but

what happens when your site just doesn't look right and

there's no error message to tell you where the problem is?

We'll look at that in the next video.