Week 2 Classwork Solutions

WeekTwoCW.java

/**
 * This class contains the solutions to
 * the Week 2 classwork exercises.
 */
public class WeekTwoCW {

    public static void main(String[] args) {

        /////////////////////////////
        // Short Answer Questions //
        ///////////////////////////

        /* 1. Explain the difference between 2, 2.0, "2", and "2.0"

        Review: There are 4 main data types you should know:
        int, double, char, and String.

        - Ints (or integers) are whole numbers like -2, 0, 1, or 2.
        They can be positive or negative.
        - Doubles (or decimal numbers) are real numbers like -2.41, 7.86,
        or 1293.5. They can also be either positive or negative.
        - Chars are single characters that you see on your keyboard
        like 'A', 'b', '@', or '#'. Some examples are letters or common
        symbols. In order to make a char variable, you have to use single
        quotes which look like ' ' not " ".
        - Finally, Strings are sequences of characters. In other words, they
        are a lot of characters combined together. For example, "Hello" is
        made from the 'H', 'e', 'l', and 'o' characters.

       Answer:
       - 2 is an integer. Alternative answers: 2 could also be a byte, short, or long variable
       - 2.0 is a double. Alternative answer: 2.0 could also be a float variable
       - "2" is a String. If it was '2' instead of "2" it would be a character
       - "2.0" has to be a String.

       It is very important to understand these differences because even though we think
       all of these (above) mean the same thing (2 is a number), the computer thinks that these
       are all different values.

       Below are examples
         */

        // part 1
        int apples = 2;
        byte oranges = 2; // alternative answer
        short berries = 2; // alternative answer
        long bananas = 2; // alternative answer

        // part 2
        double cost = 2.0;
        float price = 2.0f; // alternative answer

        // part 3
        String str = "2";

        // part 4
        String str2 = "2.0";

        /* 2. Cast an integer to a double, and a double to an integer. What happens?

        If you cast an integer variable to a double, you do not lose any information.
        This is called widening casting.

        If you cast a double variable to an integer, that number is truncated - that means
        whatever comes after the decimal place is ignored.

        Run the program and see what happens to these variables:
         */

        System.out.println("\nShort Answer Question 2:\n"); // to separate Problems

        int p = 14;
        double r = 19.7;

        // Cast integer to double
        double new_p = p;

        // Cast double to integer;
        int new_r = (int) r;

        System.out.println("The old p value is " + p);
        System.out.println("The new p value is " + new_p);
        System.out.println("The old r value is " + r);
        System.out.println("The new r value is " + new_r);

        // Note that when we cast a double to an integer, it does NOT round the number.
        // So even if our double is 14.9999, if you cast it to an integer you will get 14.

        /* 3. Create a program that says “hello my name is [insert name] I am [insert age]
        years old and I want to study [insert field] when I get older”

        Note: Try doing this using variables, not just typing the entire phrase into the
        System.out.print();
         */

        System.out.println("\nShort Answer Question 3:\n"); // to separate Problems

        String name = "Rumaisa";
        int age = 17;
        String field = "robotics";

        System.out.println("hello my name is " + name + ". I am " + age +
                " years old and I want to study " + field + " when I get older.");

        System.out.println("\nClasswork Problem 1\n"); // to separate Problems

        //////////////////////////////////////////////////////////////
        // Classwork Problem 1: Using Variables & Print Statements //
        ////////////////////////////////////////////////////////////

        // Using the following variables, output in the console
        // the sum, subtraction, product, and quotient of a and b. Do the
        // same for x and y.

        int a = 20;
        int b = 11;
        double x = 5.34;
        double y = 3.4;

        int sum1 = a + b;
        double sum2 = x + y;
        System.out.println("Adding:");
        System.out.println("a + b = " + sum1);
        System.out.println("x + y = " + sum2);

        int sub1 = a - b;
        double sub2 = x - y;
        System.out.println("Subtracting:");
        System.out.println("a - b = " + sub1);
        System.out.println("x - y = " + sub2);

        int product1 = a * b;
        double product2 = x * y;
        System.out.println("Multiplying:");
        System.out.println("a * b = " + product1);
        System.out.println("x * y = " + product2);

        int quotient1 = a / b;
        double quotient2 = x / y;
        System.out.println("Dividing:");
        System.out.println("a / b = " + quotient1);
        System.out.println("x / y = " + quotient2);

        int rem1 = a % b;
        double rem2 = x % y;
        System.out.println("Remainder");
        System.out.println("a % b = " + rem1);
        System.out.println("x % y = " + rem2);

        ///////////////////////////////////////////////////////
        // Classwork Problem 2: Order of Operations in Java //
        /////////////////////////////////////////////////////

        // Using what you learned about the order of operations in java,
        // make predictions for all the values below.

        // Because these numbers are complex, we will use parentheses to
        // explain the order of calculations for each value. I will write
        // detailed explanations for the first two problems.

        double h = 5.43;
        double i = 34.909;
        double j = 54.05;
        double k = 8594.4;

        double value1 = h * i + k / j;
        double value2 = h + h % k * k * j - i;
        double value3 = i / j % k % h + i * h;
        double value4 = k * j % k / k * i;
        double value5 = i * j * k % h + j * k;

        // Problem: h * i + k / j
        // h * i will be calculated first.
        // k / j will be calculated next.
        // then we will add (h * i) and (k / j)
        System.out.println("Prediction 1: " + ( (h * i) + (k / j) ));
        System.out.println("h * i + k / j = " + value1);
        System.out.println();

        // Problem: h + h % k * k * j - i
        // h % k will be calculated first.
        // next we will multiply (h % k) and k
        // then we will multiply ((h % k) * k) and j
        // then we will add h and (((h % k) * k) * j)
        // finally we will subtract i from (h + (((h % k) * k) * j))
        System.out.println("Prediction 2: " + (  (h + (((h % k) * k) * j)) - i ));
        System.out.println(" h + h % k * k * j - i = " + value2);
        System.out.println();

        System.out.println("Prediction 3: " + ( (((i / j) % k) % h) + (i * h) ));
        System.out.println("i / j % k % h + i * h = " + value3);
        System.out.println();

        System.out.println("Prediction 4: " + ( (((k * j) % k) / k) * i ));
        System.out.println("k * j % k / k * i = " + value4);
        System.out.println();

        System.out.println("Prediction 5: " + ( (((i * j) * k) % h) + (j * k) ));
        System.out.println("i * j * k % h + j * k = " + value5);
        System.out.println();

    }

}