CSCI A201/A597 Takehome Quiz Two Second Summer 2000

Note: should you find any typos please check with the book, as mentioned in class these questions are a selection of the questions in the book (pp. 92-94).

Questions:

1. Write the following mathematical expressions in Java.

   
   
   
   

2. Write the following Java expressions in mathematical notation.

   dm = m * ((Math.sqrt(1 + v / c) / Math.sqrt(1 - v / c)) - 1);
   volume = Math.PI * r * r * h;
   volume = 4 * Math.PI * Math.pow(r, 3) / 3; 

3. What is wrong with this version of the quadratic formula?

   x1 = (-b - Math.sqrt(b * b - 4 * a * c)) / 2 * a; 
   x2 = (-b + Math.sqrt(b * b - 4 * a * c)) / 2 * a;

4. Give an example of integer overflow. Would the same example work correctly if you used floating-point? Give an example of a floating-point roundoff error. Would the same example work correctly if you used integers? When using integers, you would of course need to switch to a smaller unit, such as cents instead of dollars or milliliters instead of liters.

5. Let n be an integer and x a floating-point number. Explain the difference between

   n = (int)x;

   and

   n = (int)Math.round(x);

   For what values of x do they give the same result? For what values of x do they give different results? What happens if x is negative?

6. Find at least five syntax errors in the following program.

   public class WarmUpSix
   { public static void main(String[] args) 
     { System.out.print("This program adds two numbers.),
       x = 5; 
       int y = 3.5;
       System.out.print("The sum of " + x + " and " + y " is: "); 
       System.out.println(x + y)
     }
   }

7. Find at least three logic errors in the following program.

   public class WarmUpSeven 
   { public static void main(String[] args) 
     { ConsoleReader console = new ConsoleReader(System.in);
       int total = 1; 
       System.out.println("Please enter a number:"); 
       int x1 = Integer.parseInt(console.readLine()); 
       total = total + x1; 
       System.out.println("Please enter another number:"); 
       int x2 = Integer.parseInt(console.readLine()); 
       total = total + x1; 
       double average = total / 2;
       System.out.println("The average of two numbers is " 
         + average); 
     }
   }

8. Explain the difference between 2, 2.0, "2", and "2.0".

9. Explain what each of the following two program segments computes:

   x = 2; 
   y = x + x;

   and

   s = "2";
   t = s + s; 

10. Uninitialized variables can be a serious problem. Should you always initialize every variable with zero? Explain the advantages and disadvantages of such a strategy.

11. True or false? (x is an int and s is a String)
    • Integer.parseInt("" + x) is the same as x

    • "" + Integer.parseInt(s) is the same as s

    • s.substring(0, s.length()) is the same as s

12. Give two ways for converting a number to a string. What is the advantage of each of these ways?

13. How do you get the first character of a string? The last character? How do you remove the first character? The last character?

14. How do you get the last digit of a number? The first digit? That is, if n is 23456, how do you find out 2 and 6? Do not convert the number to a string. Hint: %, Math.log

15. What is a final variable? Can you define a final variable without supplying its value?

16. What are the values of the following expressions? In each line, assume that

    double x = 2.5;
    double y = -1.5;
    int m = 18;
    int n = 4;
    String s = "Hello";
    String t = "World"; 

    • x + n * y - (x + n) * y

    • m / n + m % n

    • 5 * x - n / 5

    • Math.sqrt(Math.sqrt(n))

    • (int)Math.round(x)

    • (int)Math.round(x) + (int)Math.round(y)

    • s + t

    • s + n

    • 1 - (1 - (1 - (1 - (1 - n))))

    • s.substring(1, 3)

    • s.length() + t.length()