Let's say someone doesn't feel fine at the moment when another person asks how he feels. But he's sure that he should feel better soon - which one is correct:
"I will be fine"
or
"I'm going to be fine"
Let's say someone doesn't feel fine at the moment when another person asks how he feels. But he's sure that he should feel better soon - which one is correct:
"I will be fine"
or
"I'm going to be fine"
Both of your examples are correct. Let me explain why.
Both of your examples are in the simple future tense. There are two forms of the simple future tense:
http://www.englishpage.com/verbpage/simplefuture.html
1. to be going to + base form of a verb (or verb1)
"I am going to be fine."
This form is usually used to talk about future plans.
"I am going to visit you soon."
"I am going to the doctor tomorrow."
2. will + base form of verb (or verb1)
"I will be fine."
This form is usually used to talk about a promise or a voluntary action.
"I will call him."
"I will stop smoking."
3. You can use either form to express a prediction.
According to http://www.englishpage.com/verbpage/simplefuture.html, when you make a prediction about the future, you can use either form (going to or will). When used in this way, the other 2 rules don't apply.
"I will be fine."
"I am going to be fine."
"I will be a doctor when I grow up."
"I am going to be a doctor when I grow up."
"I think it will rain tonight."
"I think it is going to rain tonight."
There is no difference in the meaning of these sentences!
http://www.really-learn-english.com/simple-future-exercises.html
Both are fine; they mean the exact same thing. In speech, the first is more likely to be contracted:
I'll be fine.
I also have the impression it's more common than "going to be", likely because it's shorter to say. Also of note is that in cases like this, "going to" is often spoken as one mushed-together word:
I'm gonna be fine.
This should definitely not be used in formal writing, and if you're learning the language it's best to clearly enunciate your words, but as you might hear this from a native speaker I thought it was worth mentioning.