Add Sum Digits exercise

Author: phrdang

src/com/codefortomorrow/intermediate/chapter11/practice/SumDigits.java

@@ -0,0 +1,34 @@
+package com.codefortomorrow.intermediate.chapter11.practice;
+
+/*
+Write a method that computes the sum of the digits
+in an integer. Use the following method header:
+
+public static int sumDigits(long n)
+
+For example, sumDigits(234) returns 9 (because 2 + 3 + 4). 
+
+Hint: Use the % operator to extract digits,
+and the / operator to remove the extracted digit.
+For instance, to extract 4 from 234, use 234 % 10 (= 4).
+To remove 4 from 234, use 234 / 10 (= 23).
+
+Use a loop to repeatedly extract and remove the digit
+until all the digits are extracted.
+
+Write a test program that prompts the user to enter an integer and
+displays the sum of all its digits.
+
+Bonus points for writing a JavaDoc comment for the sumDigits method.
+
+Adapted from Exercise 6.2, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class SumDigits {
+    public static void main(String[] args) {
+        // test sumDigits here
+    }
+    
+    // write sumDigits method here
+}

src/com/codefortomorrow/intermediate/chapter11/solutions/SumDigits.java

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+package com.codefortomorrow.intermediate.chapter11.solutions;
+
+import java.util.Scanner;
+
+/*
+Write a method that computes the sum of the digits
+in an integer. Use the following method header:
+
+public static int sumDigits(long n)
+
+For example, sumDigits(234) returns 9 (because 2 + 3 + 4). 
+
+Hint: Use the % operator to extract digits,
+and the / operator to remove the extracted digit.
+For instance, to extract 4 from 234, use 234 % 10 (= 4).
+To remove 4 from 234, use 234 / 10 (= 23).
+
+Use a loop to repeatedly extract and remove the digit
+until all the digits are extracted.
+
+Write a test program that prompts the user to enter an integer and
+displays the sum of all its digits.
+
+Bonus points for writing a JavaDoc comment for the sumDigits method.
+
+Adapted from Exercise 6.2, Introduction to Java Programming (Comprehensive),
+10th ed. by Y. Daniel Liang
+*/
+
+public class SumDigits {
+    public static void main(String[] args) {
+        // prompt user for integer
+        Scanner input = new Scanner(System.in);
+        System.out.print("Enter an integer: ");
+        long n = input.nextLong();
+        input.close();
+
+        // print the sum of the digits in that integer
+        System.out.println("Sum of digits in " + n + ": " + sumDigits(n));
+    }
+    
+    /**
+     * Return the sum of all of the digits
+     * in the given number
+     * @param n  a number to sum the digits of
+     * @return the sum of all of the digits
+     * in the given number
+     */
+    public static int sumDigits(long n) {
+        int sum = 0;
+        while (n > 0) {
+            // extract last digit and add it to sum
+            sum += n % 10;
+
+            // remove the last digit
+            n /= 10;
+        }
+        return sum;
+    }
+}