Computer Science - 2A Programming Basics

Data type

Data type

indicates the type of data that can be stored in a field

Typical memory usage: integer

2 bytes

Typical memory usage: float/real

4 bytes

Typical memory usage: character

1 byte

Typical memory usage: string

1 byte per character

Typical memory usage: boolean

theoretically 1 bit, usually 1 byte in high level languages

Constant

a value that does not change in a program

How are constants written?

in capitals, if space, use underscore

Snake case

the way constants are written

How do we declare constants in Python?

(no way to make unchangeable variable)
[IDENTIFIER] = [value]

How do we declare constants in pseudocode?

CONSTANT [IDENTIFIER] ← [value]

Why declare a constant? [2]

- prevents value from being accidentally changed by code
- shows programmer that value should remain the same

Can a constant change its value? [2]

- not while the program is running
- can be changed before program is compiled or translated

Change a value's datatype in pseudocode [2]:

- STRING_TO_INT(x)
- x ← x as INT

Output length of string (pseudocode, Python)

string = [any string]
- OUTPUT(LEN(string))
- print(len(string))

Output substring (pseudocode, Python)

string = [any string]
- OUTPUT(SUBSTRING([start], [end], string))
- print(string[[start]:[end]:[step]])

Output position of character (pseudocode, Python)

string = [any string]
- OUTPUT(POSITION(string, [character]))
- print(string.rfind([character]))

Concatenate string (pseudocode, Python)

string1 = [any string]
string2 = [any string]
new_string = [combination of string1 and string2]
- new_string ← string + string2
- new_string = string + string2

Concatenate

link together (strings)

Convert character to ASCII function (pseudocode)

CHAR_TO_CODE(a)

Convert to uppercase (Python)

string = [any string]
print(string.upper())

Find datatype of variable (Python)

print(type([identifier]))

Uses of comments [3]:

- describe the purpose of programs
- state program's author
- explain what code does

Common data types [5]

- integer
- float/real
- character
- string
- boolean

(check if it is) equal to

==

(check if it is) not equal to

!=

less than

<

greater than

>

less than or equal to

<=

greater than or equal to

>=

Declare a variable

defining it for the first time

Reference a variable

use the identifier in code to have in calculations or lists

Nested statements

a statement inside another statement

AND

returns True if both values are True

OR

returns True if at least one value is True

NOT

returns True if value is False

Random integer (pseudocode, Python)

- RANDOM_INT(0, 100)
- import random
random.randint(1, 100)

Definite iteration

a process that repeats a set number of times

Indefinite iteration

a process that repeats until a certain condition is met

Example of definite iteration

for loops

Example of indefinite iteration

while loops

WHILE loops have the condition tested at the top/bottom

top

REPEAT...UNTIL loops have the condition tested at the top/bottom

bottom

Array

data structure that allows you to hold many items of data which is referenced by one identifier

Qualities of array [2]:

- fixed length
- declare length when created

Qualities of list [2]:

- variable length
- can append onto list

Output length of array (pseudocode, Python)

- OUTPUT(LEN(array))
- print(len(array))

2D array

an array of an arrays arranged in a grid format, accessed using two index values

Reference an item in a 2D array

array[i][j]

Record

data structure consisting of a number of fields which can be of different types