CS 1713/1711 Introduction to Computer Science Lecture 39

CS 1713 Lecture 39: Practice with Arrays and Loops
December 1, 1999

Example: Calculate the sum of the even number elements in the array apple. Assume apple is an array of double.
Example: Write a method:
```
    public int[] extractLargest(int [] a, int [] b)
```
This method returns an array of the same size as a and b with the largest elements (pairwise). The method returns null if a and b are not of the same size.
Example: Write a method:
```
    public void reverse(int [] a)
```
This method reverses the order of the elements in the integer array a Write the method to do the reversal in place without allocating another array. Draw a picture of an array with an odd number of elements and one with an even number of elements to make sure that you have the indexing correct.
Example: A palindrome is a string that reads the same forwards as backwards. The famous quote Able was I ere I saw Elba is an example of a palindrome. Write a method:
```
    public boolean isPalindrome(String p)
```
This method tests to see whether the string is a palindrome. Ignore the difference between upper and lower case letters by converting p to lower case before doing the test. (The String class has toLowerCase and toUpperCase methods.) Notice the similarity between this problem and reverse. The indexing is the same.
Example: Create an n by n identity matrix. An identity matrix is a two-dimensional array with n rows and n columns. All of the elements are 0 except the diagonal elements which have 1's in them. Draw a picture before writing the code.
Example: Write a method that outputs a centered triangular pattern. It takes the number of lines on which to output. If there are n lines, the pattern is 2n+1 characters wide. The following is an example for n of five:
```
-----*-----
----***----
---*****---
--*******--
-*********-
***********
```
Hint: the outer loop controls the line number. The inner loop controls what is printed on the i-th line.
Example: Write a method:
```
     public void printBoxed(String p)
```
This method prints p within a box. There is one blank before the string and one blank after. For example the string Introduction would be printed:
```
****************
* Introduction * 
****************
```

Objective: More practice with arrays and loops.

Last revision: November 28, 1999 at 8:30 am