FirstAndLastDigitSum.java

// Write a method named sumFirstAndLastDigit with one parameter of type int called number.  

// The method needs to find the first and the last digit of the parameter number passed to the method, using a loop and return the sum of the first and the last digit of that number.  

// If the number is negative then the method needs to return -1 to indicate an invalid value.  

// Example input/output  

// sumFirstAndLastDigit(252); → should return 4, the first digit is 2 and the last is 2 which gives us 2+2 and the sum is 4.
//  sumFirstAndLastDigit(257); → should return 9, the first digit is 2 and the last is 7 which gives us 2+7 and the sum is 9.
//  sumFirstAndLastDigit(0); → should return 0, the first digit and the last digit is 0 since we only have 1 digit, which gives us 0+0 and the sum is 0.
//  sumFirstAndLastDigit(5); → should return 10, the first digit and the last digit is 5 since we only have 1 digit, which gives us 5+5 and the sum is 10.
//  sumFirstAndLastDigit(-10); → should return -1, since the parameter is negative and needs to be positive.
 

public class FirstAndLastDigitSum
{
    public static int sumFirstAndLastDigit (int num)
    {
        if (num < 0)
            return -1;
        int first = 0, last = num % 10;
        num = num / 10;
        
        while (num != 0)
        {
        	if (num / 10 == 0)
	            first = num % 10;
	        num = num / 10;
        }
        return first + last;
    }

    public static void main (String[]args)
    {
        System.out.println (sumFirstAndLastDigit (352));
        System.out.println (sumFirstAndLastDigit (1));
        System.out.println (sumFirstAndLastDigit (-7));
    }
}