The other answers are correct. However, I thought I'd add an interview which Nicola Sturgeon, leader of the SNP, gave within the last week which clearly answers this part of the question.
This is a lengthy exchange but it gives the SNP's current response that this line of questioning very directly.
Interviewer: You're also setting out a new plan for the currency. You now want a new Scottish currency after independence. There's been some confusion about how the Euro would fit into that picture. The opposition is that Scotland would have to commit to join the Euro but wouldn't necessarily ever intend to do so. Is that right?
Nicola Sturgeon: Well, Channel 4 have, I think, with the greatest respect, got this slightly wrong in the recent past. You only have to look at countries already within the European Union. Sweden, which joined the European Union after the commitment to be in the Euro was in place and is not in the Euro, has no intentions of joining the Euro and the European Union has no intentions of trying to force them into the Euro. Jean-Claude Juncker is on record as saying it's not the business of the EU to force any country into the Euro. So this argument that Scotland would somehow have to be in the Euro simply doesn't bear up under any scrutiny.
Interviewer: You're quite right. Sweden isn't in the Euro and shows no intention of joining any time soon. But they have committed to joining the Euro, as have the Czech Republic, Hungary, Poland, Romania, Bulgaria and Croatia. None of them in the Euro, but they've all committed to joining the Euro. So, just for clarity so that people understand, you would commit to joining the Euro but you have no intention of actually doing so?
Nicola Sturgeon: Well, we would have discussions with the European Union about the basis of an independent Scotland's membership but...
Interviewer: But those are the rules, First Minister.
Nicola Sturgeon: I think what people have a right to know is, could Scotland be forced to go into the Euro? And that's the fundamental point. None of these countries that you have just read out to me there...there is absolutely no suggestion by anybody that if they don't want to go into the Euro that anybody will force them to go into the Euro.
Interviewer: Absolutely. And Bulgaria have actually told us that they could stay out of the Euro indefinitely.
Nicola Sturgeon: Well, isn't that the key point?
Interviewer: But they've also said that they're committed to joining the Euro, which are the rules of membership. So you would be committed to joining the Euro. You don't seem to be willing to say that for some reason. Maybe you think it's politically toxic to do so?
Nicola Sturgeon: Well, it's not politically toxic.
Interviewer: Well, then say it.
Nicola Sturgeon: You have demonstrated that it doesn't mean very much. If countries say, "Well, we've committed to something but everybody knows that there's no way of forcing us to do it."
Interviewer: If it doesn't mean very much then you should have no objections to saying, "Those are the rules. That's what we'll do. We'll do the same as everybody else."
Nicola Sturgeon: I'm not going to sit here right now and anticipate the discussion and the details of the discussion that we would have with the European Union. The fundamental thing for Scotland is that we couldn't be forced to be in the Euro, and I think that's what most people in Scotland would want to hear me address.
The short answer is that the SNP do not believe that Scotland would have to join the Euro after independence. Clearly, they can point to other countries in the EU which don't have to opt-outs which the UK and Denmark have but which are nevertheless not in the Eurozone. Sturgeon is at pains to argue that Scotland could stay out of the Euro if it wants just like these other countries. As she says, the requirement to join the Euro "doesn't mean very much". She probably appreciates that Scotland would technically be required to commit to membership. As the interview demonstrates, she clearly isn't willing to state that publicly.
As the other answers state, the main reason for focusing on currency plans is to try and convince sceptical No voters for whom currency was a stumbling block to voting Yes in 2014. Broadly speaking, the SNP believe that if they can satisfy the concerns of people on currency and talk up the threat of Brexit that they have a good chance of winning a future independence referendum.
Since they don't believe that the EU's rules on Euro membership could for much their preferred option is now a new Scottish currency, not the Euro.