Sum of First and Last Digit of a Number in Java

Previously we have written a Java program to find the sum of digits of the given number. Now in this post, we will write a Java program to find the sum of the first and last digit of a number.

Example:-
Number = 12345
The first digit = 1, last digit = 5
Sum of first and last digits = 1 + 5 = 6

Procedure to find the sum of first and last digit of a number in java,

  • Take a number
  • Declare sum variable and initialize it with 0
  • Find the last digit. To find the last digit we can use % operator. The expression number%10 gives the last digit of the number.
  • Find the first digit of the number. For this
    • Find the total number of digits in the given number.
    • Divide the number by 10^(total_number_of_digits-1), it will give the first digit of the number.
  • Add first and the last digit to the sum variable.

How to find or get the last digit of a number in java?

You can easily find the last digit of a number in Java using % operator. Any number%10 gives the last digit of the number. Below code in Java is used to get the last digit of a number,

int number = 1234;
int last_digit = number % 10;

So, last_digit = 1234 % 10 = 4

How to find or get the first digit of a number in Java?

To find or get the first digit of a number in Java, First of all, we need to count the total number of digits in the given number.

int number = 1234;
So, total_digits = 4;

After calculating number of digits, calculate the power of 10 ^ (total_digits-1)

int divisor = (int) Math.pow(10, total_digits-1);
int first_digit = number / divisor;

So, divisor = (int)Math.pow(10, 3) = 1000

The return type of the pow(-,-) method of Math class is double. We are working with integer values so convert it into an integer using type-casting. You can also use your own method to find the power of a given number. Now, divide the number using the power value.

So, first_digit = 1234 / 1000 = 1

Java Program to find the sum of first and last digit of the number

import java.util.Scanner;

public class SumOfFirstAndLastDigitProgram {

  // method to find sum of first and last digit
  private static int FirstLastDigitSum(int number) {

     // declare variables
     int lastDigit, firstDigit, divisor;;
     int totalDigits = 0;
     int sum = 0;

     // find last digit
     lastDigit = number%10;

     // find total number of digits
     totalDigits = findDigits(number);

     // calculate divisor value
     divisor = (int)Math.pow(10, totalDigits-1);

     // find first digit
     firstDigit = number / divisor;

     // add values
     sum = firstDigit + lastDigit;

     return sum;
  }

  // method to find total number of digits
  private static int findDigits(int number) {
     int count = 0;
     while(number!=0) {
        count++;
        number = number/10;
     }
     return count;
  }

  public static void main(String[] args) {

     // declare variables
     int number = 0;
     int sum = 0;

     // create Scanner class object 
     // for reading the values
     Scanner scan =  new Scanner(System.in);

     // read input
     System.out.print("Enter an integer number:: ");
     number = scan.nextInt();

     // find sum of digits of number
     sum = FirstLastDigitSum(number);

     // display result
     System.out.println("The sum of first & last"
            +" digit of the number "+number
            +" = "+ sum);

     // close Scanner class object
     scan.close();
  }
}

The output for the different test-cases:-

Enter an integer number:: 213457
The sum of first & last digit of the number 213457 = 9

Enter an integer number:: 456
The sum of first & last digit of the number 456 = 10

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