Example 1: Count Number of Digits in an Integer using while loop

public class NumberDigits{

    public static void main(String[] args){

        int count = 0, num = 3452;

        while(num != 0)
        {
            // num = num/10
            num /= 10;
            ++count;
        }

        System.out.println("Number of digits: " + count);
    }
}

Output

Number of digits: 4

In this program, while the loop is iterated until the test expression num != 0 is evaluated to 0 (false).

• After the first iteration, num will be divided by 10 and its value will be 345. Then, the count is incremented to 1.
• After the second iteration, the value of num will be 34 and the count is incremented to 2.
• After the third iteration, the value of num will be 3 and the count is incremented to 3.
• After the fourth iteration, the value of num will be 0 and the count is incremented to 4.
• Then the test expression is evaluated to false and the loop terminates.

Example 2: Count Number of Digits in an Integer using for loop

public class NumberDigits{

    public static void main(String[] args){

        int count = 0, num = 123456;

        for(; num != 0; num/=10, ++count) {   
        }

        System.out.println("Number of digits: " + count);
    }
}

Output

Number of digits: 6

In this program, instead of using a while loop, we use a for loop without any body.

On each iteration, the value of num is divided by 10 and count is incremented by 1.

The for loop exits when num != 0 is false, i.e. num = 0.

Since, for loop doesn’t have a body, you can change it to a single statement in Java as such:

for(; num != 0; num/=10, ++count);