[Solved] How to convert an ArrayList of Strings to integers without any library methods?

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You are missing something here. You have a List of Strings, and you should iterate over the characters of each of these Strings separately in order to convert it to an int. This means you need two nested loops.

Though there are much easier ways of doing it (with Integer.parseInt()), here’s an implementation based on the logic of your original code:

List<String> numbers = Arrays.asList("45","9","77");
List<Integer> output = new ArrayList<>();
for (String number : numbers) {
    int res = 0;
    for (int i = 0; i < number.length(); i++) {
        res = res * 10 + (number.charAt(i) - '0');
    }  
    output.add(res);         
}
System.out.println (output);

Output:

[45, 9, 77]

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solved How to convert an ArrayList of Strings to integers without any library methods?