CS 12300-001 Exam 1 Review

The exam is on Wednesday, September 28.

The exam is over Chapters 1 - 3 from the textbook,
https://learn.zybooks.com/zybook/PNWCS12300KraftFall2022

The most important ideas from those chapters are in these sections.
   Sections 1.6, 1.7.
   Sections 2.1, 2.4, 2.8, 2.9, 2.13.
   Sections 3.1, 3.3, 3.8, 3.10, 3.15, 3.28.



Here are a few review problems.


Problem 1) What does the following program print out when it is run?
If there are any blank lines in the output, be sure to clearly state that.

   public class Program1
   {
      public static void main(String[] args)
      {
         System.out.print( "*" );
         System.out.print( "*\n" );
         System.out.println( "***" );
         System.out.print( "**\n*" );
         System.out.println( "*" );
      }
   }



Problem 2) What does the following program print out when it is run?
If there are any blank lines in the output, be sure to clearly state that.

   public class Program2
   {
      public static void main(String[] args)
      {
         System.out.print( "*" );
         System.out.print( "*\n" + "**" );
         System.out.println( "*\"*\"" );
         System.out.print( "\n**\n*" );
         System.out.println( "\\*\\" );
      }
   }



Problem 3) Suppose that

   String s = "one two three four";

What is the value for each of the following expressions?

(a)  s.substring(0, 4).length() + s.substring(8, 13).length()
(b)  (s.substring(0, 4) + s.substring(8, 13)).length()
(c)  s.substring(4, 7) + s.charAt(8) + s.charAt(14)
(d)  s.substring(3, 8).length()
(e)  s.substring(0, 3) + "2" + s.substring(8)
(f)  s.substring(4, 5).toUpperCase() + s.substring(5, 7)



Problem 4) What should be the data type for the variable x and the data
type for the variable y in order that the following two lines of code
compile correctly. Also, what will be the value of y after the two lines
are executed? Briefly explain your answer.

   x = "2" + 2;
   y = x + 2;



Problem 5) Assume that.
   int x =   1;
   int y =  -3;
   int z = 101;
What is the type and value for each of the following expressions?

(a)   3 * z - y / x
(b)   (2.0 + x) / (1 - y)
(c)   x + 2 <= y
(d)   x + y + "z"
(e)   x + (y + "z")



Problem 6) Suppose the String variable ssn holds a social security number
in the form "xxx-xx-xxxx". Define a String variable ssn2 whose value is the
last four digits of the social security number contained in ssn.



Problem 7) Suppose the String variable pn is a phone number in the form
"xxx-xxx-xxxx". Define a String variable pn2 whose value is the phone
number contained in pn converted into the format "(xxx) xxx-xxxx". So, as
an example, the string "219-989-2273" would be converted to "(219) 989-2273".
You can assume that the phone number in pn is formatted correctly.



Problem 8) Suppose the String variable pn is a phone number in the form
"(xxx) xxx-xxxx". Define a String variable pn2 whose value is the phone
number contained in pn converted into the international format
"+1-xxx-xxx-xxxx". So, as an example, the string "(219) 989-2273" would
be converted to "+1-219-989-2273". You can assume that the phone number
in pn is formatted correctly.



Problem 9) Give the output of the following program segment if:
(a)  x=1 and y=1,
(b)  x=2 and y=2.

   if (x > 1) {
      if (y > 2) {
         System.out.println(2*x-y);
      } else {
         System.out.println(2*x+y);
      }
   } else {
      if (y > 2) {
         System.out.println(x-y);
      } else {
         System.out.println(x+y);
      }
   }



Problem 10) Explain all the possible values that the variable w can
have after the following code is executed. Assume that u and v are
int's defined elsewhere in the program.

   int w = 0;
   if (u > 0) w++;
   if (v > 0) w++;



Problem 11) Explain all the possible values that the variable w can
have after the following code is executed. Assume that u and v are
int's defined elsewhere in the program.

   int w = 0;
   if (u > 0)
   {
      w++;
   }
   else if (v > 0)
   {
      w++;
   }



Problem 12) Consider the following code fragment.

   if ( p < 0 )  { System.out.println( "p is negative" ); }
   if ( p == 0 ) { System.out.println( "p is zero" ); }
   if ( p > 0 )  { System.out.println( "p is positive" ); }

Rewrite this code fragment using an if-elseif-else-statement.




Problem 13) What is printed out by the following code fragment?

   int n = 15;
   if ( n >= 10 && n <= 20 )
   {
      System.out.println( "A" );
   }
   else
   {
      System.out.println( "B" );
   }
   if ( n < 10 || n < 20 )
   {
      System.out.println( "C" );
   }
   else
   {
      System.out.println( "D" );
   }
   if ( !(n < 100) )
   {
      System.out.println( "E" );
   }
   if ( (n == 25) || (n != 15) )
   {
      System.out.println( "F" );
   }
   if ( !( (n != 100) && (n < 50) ) )
   {
      System.out.println( "G" );
   }
   else
   {
      System.out.println( "H" );
   }



Problem 14) What is printed out by the following code fragment?
Also, indicate which of the following boolean operators get
short circuited (see Section 3.16
   https://learn.zybooks.com/zybook/PNWCS12300KraftFall2022/chapter/3/section/16
and Section 3.42
   https://learn.zybooks.com/zybook/PNWCS12300KraftFall2022/chapter/3/section/42
in the textbook).

   boolean b1 = true;
   boolean b2 = false;
   if ( b1 || !b1 )
   {
      System.out.println("One.");
   }
   if ( !b1 && b1 )
   {
      System.out.println("Two.");
   }
   if ( !b2 && b1 )
   {
      System.out.println("Three.");
   }
   if ( !(b1 || !b2) )
   {
      System.out.println("Four.");
   }
   if ( !(b1 && b2) )
   {
      System.out.println("Five.");
   }
   if ( (!b2 || b1) && b1 )
   {
      System.out.println("Six.");
   }



Problem 15) Find and correct the error in the following if-statement.

   if ( 0 <= x <= 5 )
   {
      System.out.println( "x is between 0 and 5" );
   }



Problem 16) Find and correct the error in the following if-statement.

   if ( x && y == 0 )
   {
      System.out.println( "x and y are both zero" );
   }



Problem 17) Explain what the following program segment does.
Then add a pair of braces so that what the resulting code
prints out is always correct.

   if ( x == y )
      if ( x == 0 )
         System.out.println("x and y are both zero");
      else
         System.out.println("x and y are not equal");



Problem 18) Suppose that n is a number that must be between 0 and 50.
Rewrite the following nested if-else-statement so that it does the
same thing but is easier to understand. (Hint: Use a number line to
figure out what this code is doing.)


   if ( n > 40 )
   {
      System.out.println( "plum" );
   }
   else if ( n <= 10 )
   {
      System.out.println( "apple" );
   }
   else if ( n > 30 )
   {
      System.out.println( "pear" );
   }
   else if ( n <= 20 )
   {
      System.out.println( "banana" );
   }
   else
   {
      System.out.println( "grape" );
   }



Problem 19) What is wrong with the following program?
Describe the error and show a way to fix it.

   import java.util.Scanner;
   public class Program19
   {
      public static void main(String[] args)
      {
         Scanner in = new Scanner(System.in);
         int age = in.nextInt();
         boolean adult;
         if (age < 21)
         {
            adult = false;
         }
         System.out.println(adult);
      }
   }



Problem 20) Simplify the code in the following program as much as you can.
(Hint: Use a number line to determine what are the mutually exclusive cases.)

   import java.util.Scanner;
   public class Program20
   {
      public static void main(String[] args)
      {
         Scanner in = new Scanner(System.in);
         double n = in.nextDouble();
         if (n < 0)
         {
            System.out.println( -1 );
         }
         else if (0 <= n && n <= 1)
         {
            System.out.println( 0 );
         }
         else if (n > 1)
         {
            System.out.println( 1 );
         }
         else
         {
            System.out.println( 42 );
         }
      }
   }