Question: I am creating a applet in java where the user enters some data into four different four different text fields, clicks a button, and the data is taken from those fields and stored in a text field next to it. 

I have a button made, and it implements ActionListener, just not sure how to get the text from the four fields into the one field together.

Answer: 
In C++ language (just like in C) each declaration can include multiple declarators. E.g.

```
int a, b, c;

```

declares (and defines) three variables: `a`, `b` and `c` of type `int`. You can optionally add initializers to some declarators (or to all of them)

```
int a = 5, b, c;

```

Your 

```
nodeptr p = start, n;

```

is exactly the same thing. It declares (and defines) two variables: `p` and `n`. `p` has an initializer, `n` doesn't. So, your assertion that `n` is "not defined" is obviously not true.
It is perfectly legal declare multiple variables in a single line of code. However note that in you example both start and n will be of type nodeptr. However you cannot have something like this:
int a, float b, double c; //this is illegal