Module 04: Iteration

Question 1

What would the method call myMethod(“Karel The Dog”, ‘e’) output?

Answer 1

3

Question 2

What kind of error would the method call myMethod(“Frog”) cause?

public void myMethod(String x)

{

for(int i = 0; i <= x.length(); i++)

{

System.out.println(x.substring(i, i+1));

}

}

1. Compile Time Error: Missing return value
2. Runtime Error: String index out of range
3. Compile Time Error: Unexpected return value
4. Compile Time Error: Syntax Error in method definition

Answer 2

2. Runtime Error: String index out of range

Question 3

What will the call to the method funWithNumbers(314159) print to the screen?

Answer 3

314159

Question 4

What does the call to the method someMethod(3,1) output?

Answer 4

10

Question 5

What will the call to method patternGrid(3,4,’#’) print?

Answer 5

####

####

####

Question 6

What would the call to method divideByTen(340) output?

public int divideByTen(int num)

{

while(num / 10 >= 10)

{

num /= 10;

}

return num;

}

Answer 6

34

Question 7

Consider the following method:

What is returned as a result of the call mystery(“Lunchbox”, 4)?

Answer 7

xoxbox

Question 8

Consider the following code segment:

int x = 10;

int y = 2;

int count = 1;

while(x > y)

{

x /= y;

count++;

}

What will the value of count be after executing the code segment?

Answer 8

3

Question 9

What will the final result be when run in the console?

Answer 9

* * * *

* * *

* *

*

Question 10

Consider the following code segment:

String word = “Cafeteria”;

for(/* missing condition */)

{

System.out.print(word.substring(i+1,i+2) + “ “);

}

The code segment is intended to print every other letter in the word, starting with index 0, to produce the result C f t r a. Which of the following can be used to replace /* missing condition */ so that the code segment works as intended?

1. int i = 0; i < word.length(); i+=2
2. int i = -1; i < word.length(); i+=2
3. int i = 0; i < word.length(); i++
4. int i = -1; i <= word.length(); i+=2
5. int i = word.length() - 1; i < -1 ; i-=2

Answer 10

2. int i = -1; i < word.length(); i+=2

Question 11

Consider the following code segment:

Which of the following for loops would return the same value if System.out.println(sum) were printed?

III only

II, III and IV

II only

II and III

III and I

Answer 11

II and III

Question 12

Consider the following method:

What would the value of sum be after the method call countPs(“Peter Piper picked a pack of pickled peppers”)?

Answer 12

9

Question 13

How many times will the word “Heyo!” be printed in the following code segment?

Answer 13

15

Question 14

Consider the following code segment:

int num = 8;

for(int i = num; i > 0; i -= 3) //Line 2

{

System.out.print(“ “ + i + “ “);

}

Which of the following best explains how changing i > 0 to i >= 0 will change the result?

1. An additional value will be printed, as the for loop will iterate one additional time.
2. There will be no change in the program because the for loop will iterate the same number of times.
3. One fewer value will be printed, as the for loop will iterate one fewer time.
4. This program will result in an infinite loop, as the condition will never be false.

Answer 14

2. There will be no change in the program because the for loop will iterate the same number of times

Question 15

Consider the following method:

What value word would be printed as a result of the call mix(“Hippopotamus”, “p”)?

Answer 15

Hi0o0tamus

Question 16

Consider the following incomplete code segment, which is intended to increase the value of each digit in a String by one. For example, if num is 12345, then the resulting String would be 23456.

Which of the following should replace /* Missing Loop Header */ so that the code segment works as intended?

1. counter < num.length() - 1
2. counter <= num.length()
3. counter < num.length()
4. counter > num.length()
5. counter < num.indexOf(counter)

Answer 16

3. counter < num.length()

Question 17

Consider the following code segment:

Which of the following best explains the result of changing j < 4 to j > 4 on line 1?

1. The numbers will be printed in reverse order compared to the original because the outer loop will occur in reverse order.
2. The program will produce the same result, as the number of iterations in the outer loop hasn’t changed.
3. An infinite loop will occur because the termination of the loop will never be reached.
4. No output will be produced, as the boolean condition will never be met in the outer for loop.

Answer 17

4. No output will be produced, as the boolean condition will never be met in the outer for loop

Question 18

What, if anything, is printed as a result of executing this statement?

1. 150
2. 310
3. 10204080
4. 10204080160
5. There will not be any result printed, as ints cannot be converted to type String.

Answer 18

3. 10204080

Question 19

What are while loops?

Answer 19

while (boolean expression)

{

//code executes until false

}

Question 20

What are infinite loops?

Answer 20

Occurs when the expression in a while loop never evaluates to false. The program continues to run infinitely

Question 21

What is the purpose of “break?”

Answer 21

Breaks out of a while loop and executes statement that immediately follows while loop

Question 22

What is the purpose of return?

Answer 22

Keyword used in methods to return a value back to the initial program that called the method

Question 23

How can you avoid infinity loops?

Answer 23

1. Add a condition to the while loop
2. Add a “break” statement
3. Add a return keyword

Question 24

What are for loops?

Answer 24

• Another tool we can use to repeat code sequences
• for loops allows repeating a set of statement a specfic number of times!

for(variable initialization; boolean expression; increment)

{

//will execute if boolean is true, and until the boolean expression is false

}

• variable initialization: The initialization; this variable controls the for loop execution
• boolean expression: if the expression is false, the for loop will not execute
• increment: changes the value of the loop control variables

Question 25

What is “off by one error?”

Answer 25

When a for loop iterates one too few or one to many times, it’s referred to as an Off by One Error

Question 26

What is the difference between for and while loops?

Answer 26

While loops work better for programs with undetermined amounts of iterations

For loops are best for programs with a predetermined number of iterations

Question 27

What are string transversals?

Answer 27

• The substring() method is particularly useful when attempting to traverse Strings
• TRAVERSING is the process of going through a String one character at a time, often using loops

General String Traversal:

for(int i = 0; i < string.length(); i++)

{

String character = string.substring(i, i+1);

}

Question 28

How can you transverse a string using charAt()?

Answer 28

• We can also use chartAt(int index) to access individual characters in a String

General String Traversal:

for(int i = 0; i < string.length(); i++)

{

char character = string.charAt(i);

}

Question 29

How do you transverse a string to determine how many characters are upperclass?

Answer 29

public int numUpperCase(String string)

{

int counter = 0;

for(int i = 0; i < string.length(); i++)

{

char character = string.charAt(i); //iterates through each character if(isUpperCase(character))

//if the character is uppercase, add one to counter

{

counter++;

}

}

return counter;

}

Question 30

How do you transverse a string to replace a substring with another substring?

Answer 30

Question 31

How do you transverse a string to create this method using a while loop?

Answer 31

Using the indexOf() method, we will continue to check the string while the String to remove is in string

Question 32

How do you create a method that reverses the order of a string?

Answer 32

Question 33

What does “\t” do?

Answer 33

Inserts a new tab at specific point in the text

Question 34

What are nested loops?

Answer 34

📎 Putting a loop inside another loop in called nesting

The number of times a nested loop will run is calculated by the number of iterations in the inner loop * iteration of the outer loop

Question 35

What is an algorithm?

Answer 35

Step-by-step process that solves a problem

Question 36

What is the statement execution count?

Answer 36

The number of times a statement is executed by the program

Question 37

What is Big-O Notation?

Answer 37

A way to represent how long an algorithm will take the execute helps to determine how efficient different approaches are.

Question 38

What makes a good algorithm?

Answer 38

1. Correctness
2. Efficiency (run time and memory requirements)
   
   • Important because it affects program speed, and program cost
3. Easy to understand by someone else

Question 39

What is Efficiency Cost in algorithms?

Answer 39

📎 An efficient algorithm is one that makes economical use of processing time and computer money

Questions Asks:

1. How long does it take to perform this task?
2. Is there another approach that will get the answer more quickly?

Running a computer uses CPU Processing Time

• Processing Time is the amount of the time the computer spends processing program instructions
• Computer has a limit to its CPU usage at any given time Computer slows down when computer reaches it upper limit - when applications use to much processing time

Speed also affects program cost

• Serves cost money to run - more CPU usage, the most servers cost
• Limiting process time reduces CPU usage, and can save money on server cost

Question 40

How do you measure algorithmic performance?

Answer 40

📎 Important to be able to measure (or make an educated guess) about the space and time needed to execute an algorithm = able to compare alternative approaches to a problem you need to solve

• Absolute time of an algorithm can’t be predicted: