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How to count the number of digits in an int value?

Given the following code.

 int[] eg = {21,20,1,12,2}
 public numbers(int[] eg)
 {
     for(int i=0; i < eg.length; i++)

I would expect there to eg.length

be 5, where eg[0]

would be = 21 eg[1]

would be = 20, eg[3]

would be = 1

I would like to check each element, eg [i] to see if it is a 1-digit or 2-digit number, which I tried to eg[0].length

no avail, but can I assume this is only for lists of arrays?

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5 answers


Convert number to string and get length.

int length = String.valueOf(eg[i]).length();

or

int length = Integer.valueOf(eg[i]).toString().length();


Use this math equation (assuming all data in the array is strictly positive numbers).

int length = (int)(Math.log10(eg[i])+1);
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eg[i]

is of a type int

that has no property length

.

There are many ways to find out how many digits a number has:



  • write your own method that accepts int

    and continues to divide by 10 until the number reaches 0.

  • using math properties:

    int length = (int) (Math.log10(number) + 1);

  • converting a number to a String and using its methods

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There is an algorithm used in the JDK that is probably the fastest:

final static int [] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999,
                                  99999999, 999999999, Integer.MAX_VALUE };

// Requires positive x
static int stringSize(int x) {
    for (int i=0; ; i++)
        if (x <= sizeTable[i])
            return i+1;
}
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If you want to see what the length of the number is, MChaker's solution is correct. However, if you want to know if a number contains a digit or a digit more than one digit, you can consider the following solution:

public class NumberTest {
public static void main(String[] args) {
    int[] eg = {21,20,1,12,2, -3, -8, -20};
    System.out.println("Array Length: " + eg.length);

    for(int i=0; i < eg.length; i++) {
        System.out.println("#" + i + ": Value: " + eg[i] + " one digit number: " + isOneDigitNumber(eg[i]));
    }
}
static private boolean isOneDigitNumber(int number) {
    return (-10 < number && number < 10);
}

}

and here is the result of the above code:

Array Length: 8
#0: Value: 21 one digit number: false
#1: Value: 20 one digit number: false
#2: Value: 1 one digit number: true
#3: Value: 12 one digit number: false
#4: Value: 2 one digit number: true
#5: Value: -3 one digit number: true
#6: Value: -8 one digit number: true
#7: Value: -20 one digit number: false
#7: Value: -20 one digit number: false
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To specify one two-digit number, compare it with 10.

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