CSci 2101 Lab 3: Arrays.

Due Monday February 13 at 11:59pm

Work in pairs on this lab.

30 points

Problem 1: Random sentence generator (8 points).

Write a program that has an array of articles, an array of adjectives, an array of nouns, and an array of verbs and constructs random sentences based on the scheme
article + adjective + noun + verb
For instance, the program may randomly select an article "My", an adjective "old", a noun "dog", and a verb "is walking", to make a sentence "My old dog is walking".
Make sure to have at a different number of elements in different arrays (for instance, you would probably have fewer articles than nouns).
Write methods as needed; avoid code repetition (if you repeat roughly the same code, make it into a method).

Problem 2: tabulating results of a two-dice roll (10 points).

Write a program that simulates 500 rolls of two six-sided dice. Create an array of integers to count how many times each sum occurs. For instance, if you get 3 on the first die and 5 on the second one, then the result is 8, and the array element that counts the number of 8s needs to be incremented. At the end print out how many times each sum occurred. In comments write your conclusions about probabilities of different sums.

Problem 3: count negative elements (6 points)

Write and test a method countNegatives that takes an array of integers (i.e. elements of type int) and returns the number of negative elements in the array.

Problem 4: reverse strings (6 points)

Write and test a method reverseStrings that takes an array of strings and changes all the strings in that array to their reverses (such as changing "apple" to "elppa").
The strings need to be changed in the orginal array. The return type of the method is void.

Extra credit: what's wrong with this program? (4 points)

This program seems to produce an unexpected result. Please explain what's happening and why.


public class Lab3Example {

    public static void main(String[] args) {
	// Should be 2000, right? 
	System.out.println(method(100l));
    }
	
    public static long method(long n) {
	for (int i = 0; i < 999; ++i) {
	    n = n + 1;
	}
	return n;
    }
}

How to submit

Submit the java file(s) by e-mail to me. The subject of the message must be 2101 Lab 3. Make sure to CC your group partner.


CSci 2101 course web site.

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