METHODS - Introduction to Java Programming - page 212

P ROGRAMMING E XERCISES

Sections 5.2-5.9
5.1

( Math: pentagonal numbers ) A pentagonal number is defined as n (3 n -1)/2 for
. . ., and so on. Therefore, the first few numbers are 1, 5, 12, 22, . . ..
Write a method with the following header that returns a pentagonal number:

n = 1, 2,

public static int getPentagonalNumber( int n)
Write a test program that uses this method to display the first 100 pentagonal num-
bers with 10 numbers on each line.

*5.2

( Sum the digits in an integer ) 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 ( 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 To remove 4 from 234, use 234 / 10
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 dis-
plays the sum of all its digits.

(2 + 3 + 4).

( = 4).

( = 23).

**5.3

( Palindrome integer ) Write the methods with the following headers

// Return the reversal of an integer, i.e., reverse(456) returns 654
public static int reverse( int number)

// Return true if number is a palindrome
public static boolean isPalindrome( int number)

Use the reverse method to implement isPalindrome . A number is a palin-
drome if its reversal is the same as itself. Write a test program that prompts the
user to enter an integer and reports whether the integer is a palindrome.

*5.4

( Display an integer reversed ) Write a method with the following header to display
an integer in reverse order:

VideoNote

Reverse an integer

public static void reverse( int number)
For example, reverse(3456) displays 6543 . Write a test program that prompts
the user to enter an integer and displays its reversal.

*5.5

( Sort three numbers ) Write a method with the following header to display three
numbers in increasing order:

public static void displaySortedNumbers(
double num1, double num2, double num3)

Write a test program that prompts the user to enter three numbers and invokes the
method to display them in increasing order.

*5.6

( Display patterns ) Write a method to display a pattern as follows:

1
2 1
3 2 1

...
n n-1 ... 3 2 1