Project Euler #2 in R - r

Question

I'm a novice at programming and I've been trying Project Euler to learn more about R.
The question that's stumping me is as follows:
Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
1, 2, 3, 5, 8, 13, 21, 34, 55, 89
By considering the terms in the Fibonacci sequence whose values do not exceed 4 million, find the sum of the even valued terms.
I've started to tackle this problem by setting the first couple numbers in the sequence:
num <- c(1, 2)
Next I'm trying to create a function fib() that will sum the last two numbers in num and append them to the vector.
My first attempt has been to do the following:
num <- c(1, 2)
fib <- function(x) {
sum <- sum(tail(x,2))
while (sum <= 4e6) {
x <- append(x, sum)
return(x)
}
}
But when I run this I only get one additional Fibonacci number:
> fib(num)
[1] 1 2 3
In turn, I tried moving return(x):
num <- c(1, 2)
fib <- function(x) {
sum <- sum(tail(x,2))
while (sum <= 4e6) {
x <- append(x, sum)
}
return(x)
}
But this seems to only create an infinite loop.
As a caveat, I'm comfortable summing the even-valued terms with a modulo and I'll do this after I work out this particular issue.
Can you point out where I'm going wrong with my code? (If you could give me a bump in the right direction without providing an explicit solution that would be even more appreciated.)
Thanks to #Minnow and #blakeoft for helping me to get a handle on this. Here's what I ended up doing to solve this problem:
SPOILER ALERT
num <- c(1, 2)
fib <- function(x) {
last2 <- sum(tail(x,2))
while (last2 <= 4000000) {
x <- append(x, last2)
last2 <- sum(tail(x,2))
}
return(x)
}
I won't include the last bit with the modulo since I want to keep the answer specific to the initial question.

Answer 1

Is this a language-specific problem? You don't really need a function, just three variables say prev, curr and next. Preload the first two and prime the even values' sum. You know how to set the value of next, then process it and shove the values back through your history.
You didn't want a specific answer, but now you have accepted one, this is what I meant - it's not r but it shows how simple it can be.
int sum = 2;
int prev = 1;
int curr = 2;
int next = 0;
while (next < 4000000) {
next = prev + curr;
if (next % 2 == 0)
sum += next;
prev = curr;
curr = next;
}
printf ("%d", sum);

Answer 2

Without giving it away:
Walk through your loop and see if you can figure out the expected output. You're close, but the sequence of events is not going to yield what you expect.