unit 2a - programming basics Flashcards
what is a variable?
a named space in memory, large enough to store a single piece of data
what is a constant?
a named space in memory with a value that can never change while the program is running
typically shown in uppercase and are separated by underscores
python DOES NOT use constants
what are the different data types?
- boolean
- character
- integer
- real
- string
what is boolean?
- can either be TRUE or FALSE
python: b = TRUE
what is a character?
- a single letter, number, space etc
python doesn’t have characters
what are integers?
- whole numbers - positive, negative or 0
python: i = 5
what is a real?
- decimal numbers
python: pi = 3.14
what is a string?
- a collection of characters (word or sentence)
python: name = “bob”
what is a declaration?
- code that causes a variable to exist
- once a variable has been declared, it can be used in the program
- you can’t use a variable before it has been declared
what is assignment?
- process of putting a value into a variable eg. i = 5
what is sequence?
- that instructions will always execute in the order in which they are written
example:
mark 1 <- 78
mark 2 <- 64
total <- mark1 + mark2
average <- total/2
OUTPUT average
what is selection?
- when a decision has to be made depending on whether the condition being tested is true or false
- IF is a common indicator of selection
example:
IF average >= 80 THEN
OUTPUT “distinction”
ELSE
OUTPUT “pass”
ENDIF
why declare a constant instead of a variable?
- prevents the value from being changed accidentally by part of code
- indicates that the value should stay constant throughout the program
can a constant ever change its value?
- a constant cannot be changed when the programming is running
- but can be changed before the program is compiled or translated
input statements in python
firstName = input (“what is your first name?”)
what are the arithmetic operators?
*
/
MOD
DIV
what is used to convert data types?
functions
what is casting?
functions being used to convert data types
what are some examples of functions?
- STRING_TO_INT(s) - converts a string s to an integer
- INT_TO_STRING(x) - converts an integer to a string
- CHAR_TO_CODE(‘a’) - evaluates to 97, using ASCII
- CODE_TO_CHAR(97) - evaluates to ‘a’, using ASCII
how do you allow a user to input a numerical value? (pseudocode)
- inputs from users are strings so they have to be converted before they can be used in a calculation eg.
OUTPUT “please enter the number of cats:”
tickets <- STRING_TO_INT(USERINPUT)
how do you allow a user to input a numerical value in python?
cats = int(input(“please enter the number of tickets:”))
what is concatenating?
joining two string variables together eg.
firstname <- “rose”
surname <- “chan”
fullname <- firstname + “ “ + surname
OUTPUT fullname
how do you identify the length of a string? (string handling functions)
LEN(str): word <- “algorithm”
OUTPUT LEN(word)
the output would be 9 because it is 9 letters long
how do you get a substring? (string handling functions)
SUBSTRING(start, end, str):
word <- “algorithm”
OUTPUT(3,6, word)
the output would be ‘orit’ because those are the letters between index 3 and 6
NOTE: strings always start their index at 0
how do you find a character’s index position?
POSITION(str,char):
word <- “algorithm”
POSITION(word, ‘r’)
the output would be 4 because ‘r’ is at index 4
how do you convert a character to ASCII using functions?
CHAR_TO_CODE(‘character’)
CODE_TO_CHAR(integer)
example: num <- CHAR_TO_CODE(‘c’)
letter <- CODE_TO_CHAR(102)
how do convert from uppercase to lowercase (and vice versa) in python?
phrase1 = “good morning”
phrase2 = “HAPPY BIRTHDAY”
print(phrase1,upper()) #”GOOD MORNING”
print(phrase2.lower()) #”happy birthday”
what are comments used for in programs?
- describing the purpose of the program
- state the author
- explaining what the code does
which symbol is used to write a comment in python?
#
what are the three basic control structures in programming?
sequence, selection and iteration
what are the three boolean operators?
AND, OR, NOT
what are the boolean comparison operators? what will the outcome always be?
= equal to
!= not equal to
> greater than
< less than
>= greater than or equal to
<= less than or equal to
the outcome of comparison expressions will always be true or false
what do IF statements do?
they allow different branches to be executed based on the result of a boolean expression
example:
IF average >= 80 THEN
OUTPUT “distinction”
ELSE IF average >=
OUTPUT “merit”
ELSE
OUTPUT “fail”
ENDIF
what is a nested if statement?
an if statement within another loop
example:
IF member = “child” THEN
IF day = “saturday” THEN
swimPrice <- 2.00
ELSE
swimPrice <- 2.50
ELSE
swimPrice <- 4.00
ENDIF
what are complex boolean expressions?
those that contain AND, OR or NOT ‘
example: IF (mark < 0) AND (mark > 100) THEN
what does the AND operator do?
returns TRUE if both conditions are TRUE
what does the OR operator do?
returns TRUE if either of the conditions are TRUE
what does the NOT operator do?
a TRUE expression become FALSE and vice versa
how do get a random number in python?
import random
die = random.randint(0,100)
print(die)
the import random will import the random library of functions
how do you get a random number in pseudocode?
die = RANDOM_INT(0,100)
OUTPUT die
what is iteration?
the repetition of a section
what are the three types of iteration statements?
FOR…ENDFOR
WHILE..ENDWHILE
DO…UNTIL (not in python)
what do FOR loops do?
used when you want the loop to execute a specific number of times
example:
total <- 0
FOR i <- 1 TO 7
dailyTemp <- USERINPUT
total <- total + dailyTemp
ENDFOR
averageWeeksTemp <- total/7
OUTPUT averageWeeksTemp
i starts at 1 and goes up to 7 adding one every time the loop is completed. loop takes place 7 times
what do WHILE loops do?
used when you want the loop to be executed WHILE a certain condition is true
example:
OUTPUT “please enter password:”
password <- USERINPUT
WHILE password != “abc123”
OUTPUT “invalid password - try again”
password <- USERINPUT
ENDWHILE
OUTPUT “correct password”
it checks the condition each time and performs the iteration if the condition is true
what does a REPEAT..UNTIL loop do?
used when you want to execute a loop until a certain condition is true. the loop will always execute once because the condition is tested at the end of the loop
example:
password <- “”
REPEAT
OUTPUT “invalid password - try again”
password <- USERINPUT
UNTIL password = “abc123”
OUTPUT “correct password”
what is an array?
a data structure that allows you to hold many different items of data that is referenced by one identifier - all items of an array must be the same data type
example: an array of 10 integers called userNames could be declared as array userNames[10]
how can information be red from or added to an array?
by using the indexes, which start at 0
how would you add an item to an array?
by referencing the specific index number
example:
array usernames[10]
usernames[0] <- “patel”
usernames[1] <- “smith”
how do you find the length of an array?
LEN(name of array) which returns the number of items in the array
can arrays be edited?
no, they have a fixed length meaning that items cannot be added.
- to add more items you would have to create a new, larger array and copy the previous items across
does python have arrays?
no, python doesn’t have an array structure. instead, it uses lists which can alter their length
how can a for loop be used to be used to output al the items in an array?
example:
FOR i <- 0 TO LEN(usernames)
OUTPUT username[i]
ENDFOR
how can a linear search be conducted on an array?
example:
OUTPUT “type in username:”
search <- USERINPUT
FOR i <- 0 TO LEN(usernames)
IF usernames[i] = search THEN
OUTPUT “name found”
ENDIF
ENDFOR
what are the advantages of using an array?
- you can easily input, sort and print many items rather than having to use lots of different variable names
what is a bubble sort?
- each item in a list is compared to the next one to it and if greater, they swap places
- at the end of the first pass the largest item is at the end and so forth
- this is repeated until all the items are sorted + another pass takes place to verify that they are in order
how do you swap items in an array?
example:
temp <- names[j]
names[j] <- names[j + 1]
names[j + 1] <- temp
what are 2D arrays?
arrays but with rows and columns
array marks[2][4] - has 3 rows and 5 columns because indexes start at 0
how do you identify an individual item in a 2D array?
example: mark[1][3]
that would output what is in row index 1 and column index 3
what is a record?
a data structure that consists of different fields which can all be of different types
example:
RECORD film
filmID: integer
title: string
yearReleased: integer
ENDRECORD
what is a field/element in a record?
a single item of data
what is instantiation?
when new instances of the record structure can be made for each new set of fields. records can be edited
example:
film1 <- new film
film1.filmID <- 232
film1.title <- “top gun”
film1.yearReleased <- 2020
OUTPUT film1.title #which will output the film title
does python have records?
no
