Chapter 5 Conditionals and Loops

Question 1

What is meant by the flow of control through a program?

Answer 1

The flow of control through a program determines the program statements that will be executed on a given run of the program.

Question 2

What type of conditions are conditionals and loops based on?

Answer 2

Each conditional and loop is based on a boolean condition that evaluates to either true or false.

Question 3

What are the equality operators? The relational operators? The logical
operators?

Answer 3

The equality operators are equal (==) and not equal (!=). The relational
operators are less than (),
and greater than or equal to (>=). The logical operators are not (!), and
(&&), and or (||).

Question 4

Given the following declarations, what is the value of each of the
listed boolean expressions?

int value1 = 5, value2 = 10;
boolean done = true;

a. value1 <= value2
b. (value1 + 5) >= value2
c. value1 < value2 / 2
d. value2 != value1
e. !(value1 == value2)
f. (value1 < value2) || done
g. (value1 > value2) || done
h. (value1 < value2) && !done
i. done || !done
j. ((value1 > value2) || done) && (!done || (value2 >
value1) )

Answer 4

Assuming the given declarations, the values are: a. true, b. true,
c. false, d. true, e. true, f. true, g. true, h. false, i. true, j. true

Question 5

What is a truth table?

Answer 5

A truth table is a table that shows all possible results of a boolean expression, given all possible combinations of variables and conditions.

Question 6

Assuming done is a boolean variable and value is an int variable, create a truth table for the expression:

(value > 0 ) || !done

Answer 6

The truth table is:

value > 0  done  !done  (value > 0) || !done
true           true    false    true
true           false   true     true
false          true    false    false
false          false   true     true

Question 7

Assuming c1 and c2 are boolean variables, create a truth table for the
expression:

(c1 && !c2) || (!c1 && c2)

Answer 7

See book 5.7.

Question 8

What output is produced by the following code fragment given the assumptions below?

if (num1 < num2)
   System.out.print(" red ");
if ((num1 + 5) < num2)
    System.out.print(" white ");
else
    System.out.print(" blue ");
System.out.println(" yellow ");

a. Assuming the value of num1 is 2 and the value of num2 is 10?
b. Assuming the value of num1 is 10 and the value of num2 is 2?
c. Assuming the value of num1 is 2 and the value of num2 is 2?

Answer 8

Based on the given assumptions, the output would be:

a. red white yellow
b. blue yellow
c. blue yellow

Question 9

How do block statements help us in the construction of conditionals?

Answer 9

A block statement groups several statements together. We use them to define the body of an if statement or loop when we want to do multiple things based on the boolean condition.

Question 10

What is a nested if statement?

Answer 10

A nested if occurs when the statement inside an if or else clause is an if statement. A nested if lets the programmer make a series of decisions. Similarly, a nested loop is a loop within a loop.

Question 11

For each assumption, what output is produced by the following code
fragment?

if (num1 >= num2)
{
   System.out.print(" red ");
   System.out.print(" orange ");
}
if ((num1 + 5) >= num2)
    System.out.print(" white ");

else
if ((num1 + 10) >= num2)
{
     System.out.print(" black ");
     System.out.print(" blue ");
}
else
    System.out.print(" yellow ");
System.out.println(" green ");

a. Assuming the value of num1 is 5 and the value of num2 is 4?
b. Assuming the value of num1 is 5 and the value of num2 is 12?
c. Assuming the value of num1 is 5 and the value of num2 is 27?

Answer 11

Based on the given assumptions, the output would be:

a. red orange white yellow
b. black blue green
c. yellow green

Question 12

Write an expression that will print a message based on the value of
the int variable named temperature. If temperature is equal to or less
than 50, it prints “It is cool.” on one line and “Dress warmly.” on the
next. If temperature is greater than 80, it prints “It is warm.” on one
line and “Dress coolly.” on the next. If temperature is in between 50
and 80, it prints “It is pleasant.” on one line and “Dress pleasantly.”
on the next.

Answer 12

if (temperature <= 50)
	 {
             System.out.println("It is cool.");
             System.out.println("Dress warmly.");
	 }
         else
               if (temperature > 80)
               {
                    System.out.println("It is warm.");
                    System.out.println("Dress cooly.");
               }
               else
              {
                System.out.println("It is pleasant.");
                System.out.println("Dress pleasantly.");
             }

Question 13

Why must we be careful when comparing floating point values for
equality?

Answer 13

Because they are stored internally as binary numbers, comparing floating point values for exact equality will be true only if they are the same bit-by-bit. It’s better to use a reasonable tolerance value and consider the difference between the two values

Question 14

How do we compare strings for equality?

Answer 14

We compare strings for equality using the equals method of the String class, which returns a boolean result. The compareTo method of the String class can also be used to compare strings. It returns a positive, 0, or negative integer result depending on the relationship between the two strings.

Question 15

Write an equals method for the Die class of Section 4.2. The method
should return true if the Die object it is invoked on has the same
facevalue as the Die object passed as a parameter, otherwise it should
return false

Answer 15

//------------------------------------------------------
// Returns true if this Die equals die, otherwise
// returns false.
//------------------------------------------------------
public boolean equals(Die die)
{
return (this.faceValue == die.faceValue);
}

Question 16

Assume the String variables s1 and s2 have been initialized. Write an
expression that prints out the two strings on separate lines in lexicographic order.

Answer 16

if (s1.compareTo(s2) < 0)
System.out.println(s1 + “\n” + s2);
else
System.out.println(s2 + “\n” + s1);

Question 17

What is an infinite loop? Specifically, what causes it?

Answer 17

An infinite loop is a repetition statement that never terminates. Specifically, the body of the loop never causes the condition to become false

Question 18

What output is produced by the following code fragment?

int low = 0, high = 10;
while (low < high)
{
System.out.println(low);
low++;
}

Answer 18

The output is the integers 0 through 9, printed one integer per line.

Question 19

What output is produced by the following code fragment?

int low = 10, high = 0;
while (low <= high)
{
System.out.println(low);
low++;
}

Answer 19

The loop is not entered, so there is no output.

Question 20

What output is produced by the following code fragment?

int low = 0, high = 10;
while (low <= high)
{
System.out.println(low);
high = high − low;
}

Answer 20

Since the value of high always remains larger than the value of low, the code loops continuously, producing many lines of zeros, until the program is terminated.

Question 21

What output is produced by the following code fragment?

int low = 0, high = 10, mid;
while (low <= high)
{
   mid = low;
  while (mid <= high)
  {
     System.out.print(mid + " ");
     mid++;
  }
 System.out.println();
 low++;
}

Answer 21

The output is:

0 1 2 3 4 5 6 7 8 9 10
1 2 3 4 5 6 7 8 9 10
2 3 4 5 6 7 8 9 10
3 4 5 6 7 8 9 10
4 5 6 7 8 9 10
5 6 7 8 9 10
6 7 8 9 10
7 8 9 10
8 9 10
9 10
10

Question 22

Assume the int variable value has been initialized to a positive integer. Write a while loop that prints all of the positive divisors of value.
For example, if value is 28, it prints divisors of 28: 1 2 4 7 14 28

Answer 22

int count = 1;
System.out.print("divisors of " + value + ":");
while (count <= value)
{
    if ((value % count) == 0)
         System.out.print(" " + count);
    count++;
}

Question 23

Assume the int variable value has been initialized to a positive integer. Write a while loop that prints all of the positive divisors of each
number from one to value. For example, if value is 4, it prints

divisors of 1: 1
divisors of 2: 1 2
divisors of 3: 1 3
divisors of 4: 1 2 4

Answer 23

int count1 = 1, count2;
while (count1 <= value)
{
       System.out.print("divisors of " + count1 + ":");
       count2 = 1;
       while (count2 <= count1)
       {
           if ((count1 % count2) == 0)
                 System.out.print(" " + count2);
          count2++;
       }
       System.out.println();
       count1++;
}

Question 24

Devise statements that create each of the following Scanner objects.

a. One for interactive input, which reads from System.in.
b. One that reads from the file “info.dat”.
c. One that reads from the String variable infoString.

Answer 24

a. Scanner user = new Scanner(System.in);
b. Scanner infoFileScan = new Scanner(new
File(“info.dat”));
c. Scanner infoStringScan = new Scanner(infoString);

Question 25

Assume the Scanner object fileScan has been initialized to read from
a file. Write a while loop that calculates the average number of characters per line of the file.

Answer 25

The following code prints out the average number of characters per line:

int numChars = 0;
int numLines = 0;
String holdLine;

// Read and process each line of the file
while (fileScan.hasNext())
{
        numLines++;
        holdLine = fileScan.nextLine();
        numChars += holdLine.length();
}
System.out.println ((double)numChars/numLines);

Question 26

What are the advantages of using an ArrayList object?

Answer 26

An ArrayList stores and manages multiple objects at one time. It allows you to access the objects by a numeric index and keeps the indexes of its objects continuous as they are added and removed. An ArrayList dynamically increases its capacity as needed.

Question 27

What type of elements does an ArrayList hold?

Answer 27

An ArrayList generally holds references to the Object class, which means that it can hold any type of object at all (this is discussed further in Chapter 8). A specific type of element can and should be specified in the ArrayList declaration to restrict the type of objects
that can be added and eliminate the need to cast the type when extracted.

Question 28

Write a declaration for a variable named dice that is an ArrayList of
Die objects.

Answer 28

ArrayList dice = new ArrayList();

Question 29

What output is produced by the following code fragment?

ArrayList names = new ArrayList();
names.add("Andy");
names.add("Betty");
names.add(1, "Chet");
names.add(1, "Don");
names.remove(2);
System.out.println(names);

Answer 29

[Andy, Don, Betty]