Part 4, loops

Question 1

what are the two terms used for a block of code repeating over and over within a program

Answer 1

1. looping

2. repetition

Question 2

what term is given to the block of code that exists within a loop

Answer 2

loop contents

Question 3

what are the three main types of loops

Answer 3

1. fixed loop
2. infinite loop
3. conditional loop

Question 4

explain what a fixed loop is

Answer 4

a fixed loop will loop a set amount of times

Question 5

explain what an infinite loop is

Answer 5

an infinite loop will have no set number of times to loop or any condition to break out the loop

note: although this type of loop is potentially infinite there are a few ways to stop it running

Question 6

what two ways might you set the number of loops on a fixed loop

Answer 6

1. variable

2. constant

Question 7

name two ways you might you stop an infinite loop

Answer 7

1. stop the program

2. have a separate script stop the script containing the infinite loop

Question 8

explain what a conditional loop is

Answer 8

a conditional loop is a type of loop that will loop until a condition has been reached

that is the condition reports true

Question 9

explain what text processing is

Answer 9

text processing is the act of a program manipulating or searching through text

note: features in a word processor such as word count is an example of text processing

Question 10

give four examples of text processing

Answer 10

1. finding the first occurrence of a word
2. finding all occurrences of a word
3. finding spelling mistakes
4. appending puncuation

Question 11

explain what an index variable is

Answer 11

an index variable is used to select an item in a list, array or string

index variables are helpful when iterating over the entirety of a list, array or string and needing to pick out an items position

when incrementing the index variable with each iteration of a loop. the index variable can be used as the position inside the string or array

Question 12

what is a sentinel value used for

Answer 12

a sentinel value is used to stop a loop, it can be used when a loop will stop but the amount of times to loop is unknown and there is no condition to stop the loop.

Question 13

give an example where a sentinel value might be useful

Answer 13

a sentinel value would be useful when taking user input

a loop could take the user input piece by piece and when the user is finished they could enter “Q”

which would be the sentinel value used to quit the loop

Question 14

what is a parallel list

Answer 14

a parallel list is two lists that have a relationship,

where the position of an item in one list is directly related to an item in another list with the same position

Question 15

when might parallel lists be useful

Answer 15

a parallel list may be useful in a situation where we need to store multiple pieces of data while maintaining the relationship of the data

Question 16

you have a specification containing words such as

“for each”, “how many”, “every”, “until”, “total”, “while”,

how might you translate these words into your algorithm

Answer 16

“for each”, “how many”, “every”, “until”, “total”, “while”,

all suggest that some sort of looping may be needed

Question 17

name 6 words you might see in a specification that suggest looping may be needed

Answer 17

1. “for each”,
2. “how many”,
3. “every”,
4. “until”,
5. “total”,
6. “while”,

Question 18

how might “how many” be translated into an algorithm”

Answer 18

“how many” assumes we need to count something so might be re written as

repeat (n) times {
if x occurs add one to the count
}

Question 19

how might “until” be translated into an algorithm

Answer 19

“until” might be re written as

repeat until (x=y)
    add 1 to y

Question 20

name 4 tests that can be used when debugging/testing lists

Answer 20

1. test lists of different lengths
2. test an empty list
3. test the first, last and mid item in the list
4. test for different sized outputs (only one output expected) (three outputs expected)