It's now a few months that I'm doing my first internship.
And I feel pretty bad.

The company is great, but the software I'm working on is horrible, bad coded and a nightmare to maintain. I think it's a common situation: fixing a bug opens other twenty bugs.
Also, the boss doesn't want to spend time to rewrite any part of it (it's not a huge thing, it would require at most three weeks).

I feel like I'm not learning almost anything and I'm not practicing anything about what I studied.
Also, when I go back home I don't have any will to code, even just to practice.

How should I feel about this? Is this a normal situation and I'm just somehow spoiled?

"it would require at most 3 weeks"

Famous last words 😂

You are not alone.

On a serious note though (prev comment was also serious, this one is just a bit more)

Maintaining old code teaches you how to read other people's code and this is a very valuable skill in software development. Don't underestimate how important it is to be able to easily navigate a code base and find what you're looking for. Trust me on this.

Stick to it mate.

@MrCSharp thanks, I'll keep this in mind

I agree with mrcsharp on maintaining old code, I would just like to add that higher level of maintaining is solving a buv without opening 20 nee oned. You should strive to getting there.
Also, about will to code after 8 hours of work: no one I know who does his job well can or wants to do it. Read tech books after work.

I'm in the pretty much the exact scenario. But I'll tell you what helped me from the previous work experience I have. Like the others said, it's actually a really important thing to pick the ability to navigate a codebase with the minimal required effort. Whenever you fix bugs, spend time in researching the best practices and enforce it as much as possible. You don't need practice for what you studied. You actually need practice on how to make design decisions (like not creating or minimising the number of bugs when you fix one in this case), considering future devs, possible upgrades, common mistakes, performance traps etc. Don't worry too much, you'll cut through in good time and start making more value for yourself and the company. :)

I guess that you are a bit of a perfectionist when it comes to code... The truth is that code can be very ugly, especially if it is old and "just works" as it always did. Do not try to fix other people's bugs if you are not asked to do so, you will get behind in your main task and neither your boss or you will be happy about it. Focusing on the main task gives you a greater sense of accomplishment, take the time at the end of your internship to improve.

for once, every coder has a different idea about what "nice looking code" looks like and secondly, when there's deadlines there's no extra time to spend on architecture. You'll see exactly these kinds of projects and code pretty much everywhere. And trust me, what feels like 3 weeks is probably more like 3 months, and you'll just introduce more new bugs to it than fix. the code there has already been tested and (even tho barely) sticks together, its rarely worth it to rewrite a big part of it unless you have seriously good reasons for it and can explain to the management that its going to save time in the long run.

also, don't expect to use a lot of what you've learned in school. Schools don't make programmers, experience makes programmers!

one big advantage of working on a badly designed project tho is that humans learn faster from bad examples than from good examples.

anyway, you're not alone, this is pretty normal