Exc-bad-instructs, how can I fix this?

You have not learnt anything in your previous questions...

When you show error message, better take more parts of the error info shown in the debug console:

Please show whole error message shown in the debug console.

The whole error message shows:

Fatal error: Unexpectedly found nil while unwrapping an Optional value: file MyPlayground.playground, line 9

Thanks for showing the message.

I guess your Playground's line 9 is at this line:

        var letter:Int = aphabet.firstIndex(of: charArray[i])!

You use forced-unwrapping `!` here, but I recommend to avoid that as far as you can.

When you want to safely-unwrap Optionals, you can use:

- Conditional binding, in short, so-called `if-let`

- Nil coalescing operator `??`

In this case, you need to define the behavior in case of `firstIndex(of:)` returning nil.

So, Conditional binding seems to be more appropriate.

Replace these two lines:

        var letter:Int = aphabet.firstIndex(of: charArray[i])!
        charArray[i] = smallCaps[letter]

with:

        if let letterIndex = aphabet.firstIndex(of: charArray[i]) {
            charArray[i] = smallCaps[letterIndex]
        }

This change prevents the runtime error Fatal error: Unexpectedly found nil while unwrapping an Optional value, but that does not mean you would get an expected result.

As I said before, `components(separatedBy:)` is not a good tool here and `charArray` cannot be an Array of characters.

You may need to rewrite your code to get Hᴇʟʟᴏ from `smallCapsFunc(text: "Hello")`.

unwrapping "by force" is always dangerous.

either use :

if let value = oprionalValue

of let value = optionalValue ?? defaultValue