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Java Program to Count the Digits in an Integer

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count digits

Java programs to count the digits in an integer have been shown here. For example, if a number is 13579, the total number of digits is 5. The algorithm, pseudocode and time complexity of the programs have also been covered below.






1. Algorithm to count the digits in an integer


1. Take a number x as input.

2. Initialize a counter to 0 say c = 0.

3. Perform x = x / 10 and Increment c by 1 i.e. c = c + 1

4. If x = 0 stop the process and display c as output else go to step 3.




2. Pseudocode to count the digits in an integer


Input : A number $n$

Output : Total no of digits in $n$

1. Procedure countDigits($n$):

2. $c \leftarrow 0$

3. If $n == 0$:

4. $c \leftarrow 1$

5. Else:

6. Repeat until $n \neq 0$

7. $n \leftarrow n / 10$

8. $c \leftarrow c + 1$

9. Return $c$

10. End Procedure





3. Time complexity to count the digits in an integer


Time Complexity: O(log(n))

Where n is the input number.





4. Program & output to count the digits in an integer




4.1. Java Program & output to count the digits in an integer using iteration

Code has been copied
/*******************************************
            alphabetacoder.com
 Java program to count the number of digits 
 in an integer using iterative approach
********************************************/

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        // declare instance of Scanner class
        Scanner sc = new Scanner(System.in);

        // declare and initialize variables
        int num = 0, count = 0;

        // take input
        System.out.print("Enter the integer = ");
        num = sc.nextInt();

        //count the digits
        if (num == 0)
            count = 1;
        else {
            while (num != 0) {
                num = num / 10;
                count++;
            }
        }

        // display result 
        System.out.print("Number of digits = " + count);
    }
}

Output

Enter the integer = 51265

Number of digits = 5





4.2. Java Program & output to count the digits in an integer using recursion

Code has been copied
/*******************************************
	     alphabetacoder.com
 Java program to count the number of digits 
 in an integer using recursive approach
********************************************/

import java.util.Scanner;

class Main {
    // recursive function to calculate
    // no of digits in an integer
    public int count_digit(int num) {
        if (num / 10 == 0)
            return 1;
        else
            // call function 
            return 1 + count_digit(num / 10);
    }

    public static void main(String[] args) {
        // declare instance of Scanner class
        Scanner sc = new Scanner(System.in);

        // declare object of Main class
        Main obj = new Main();

        // declare variables
        int num;

        // take input
        System.out.print("Enter the integer = ");
        num = sc.nextInt();

        // display result by calling recursive function
        System.out.print("Number of digits = " + obj.count_digit(num));
    }
}

Output

Enter the integer = 1122

Number of digits = 4





4.3. Java Program & output to count the digits in an integer using logarithm

Code has been copied
/************************************
          alphabetacoder.com
 Java program to count the number of
 digits in an integer using logarithm
**************************************/

import java.util.Scanner;
import java.lang.Math;

class Main {
    public static void main(String[] args) {
        // declare instance of Scanner class
        Scanner sc = new Scanner(System.in);

        // declare variables
        int num;

        // take input
        System.out.print("Enter the integer = ");
        num = sc.nextInt();

        // display result
        if (num == 0) // if input number = 0
            System.out.print("Number of digits = 1");
        else {
            // calculate result using log10
            System.out.print("Number of digits = " + (int) Math.floor(Math.log10(num) + 1));
        }
    }
}

Output

Enter the integer = 3456

Number of digits = 4




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