Why is this loop bad practice? [closed]

Question

The following loop is not good practice. Is it due to a String being the main condition of the for loop rather than an int variable, meaning the for loop is infinite? Also, is it due to there being no instance to enter 'end' to stop the loop?

Scanner in = new Scanner(System.in);
int i = 0;
for (String s = in.next(); !s.equals("end"); i++) 
{
    System.out.println("The value of i is: " + i + " and you entered " + s);
}

How can I rewrite it, so that it conforms to accepted style?

(This is a question in a past exam paper.)

Answer 1

Well your string s is never changing, which can lead to an infinite loop. You probably wanted:

for (String s = in.next(); !s.equals("end"); s = in.next(), i++) {
    ...
}

Some (me included) might say that i++ shouldn't be in the increment section of this loop, since it's not directly relevant to the condition:

for (String s = in.next(); !s.equals("end"); s = in.next()) {
    ...
    i++;
}

---

Is it due to a string being the main condition of the for loop rather than an int variable, meaning the for loop is infinite?

The original loop was indeed infinite (at least, after an initial input is entered and assuming "end" wasn't the first input). However, it's not for the reason you state. For-loops are most commonly written using integral loop control variables, but it's not always the case. For example, a common idiom for iterating through a linked list is:

for (Node node = list.head; node != null; node = node.next) {
    ...
}

The problem with your loop is that the string s is never changed, so it will never equal "end" unless that's the first input.