Computer science programming

What is a variable?

A named memory location that stores a value that can change during program execution — declared by giving it a name and assigning a value — eg x = 5

What is a constant?

A named memory location that stores a value that cannot change during program execution — declared using const — eg const pi = 3.14

Why use constants instead of variables?

Makes code easier to read and maintain — prevents accidental changes to important values — if the value needs updating you only change it in one place

What is an assignment?

Giving a value to a variable or constant using the = operator — eg name = "Sam" or score = 0

What is the difference between a variable and a constant?

A variable can change its value during the program — a constant cannot change once declared

What is sequence in programming?

Statements are executed one after another in the order they are written — the simplest and most fundamental programming construct

What is selection in programming?

The program chooses between different paths based on a condition being true or false — implemented using IF THEN ELSE or SWITCH CASE statements

What is iteration in programming?

Repeating a block of code — can be count-controlled using a FOR loop — or condition-controlled using WHILE or DO UNTIL loops

What is a count-controlled loop?

A loop that repeats a fixed known number of times — uses a FOR loop — the number of repetitions is determined before the loop starts

What is a condition-controlled loop?

A loop that repeats based on whether a condition is true or false — the number of repetitions is not known in advance — uses WHILE or DO UNTIL

What is the difference between a WHILE loop and a DO UNTIL loop?

WHILE — checks the condition before entering the loop — may never execute if condition is immediately false. DO UNTIL — checks the condition after the loop body — always executes at least once regardless of the condition

Write a FOR loop in OCR ERL that prints the numbers 1 to 10

for i=1 to 10. print(i). next i

Write a FOR loop in OCR ERL that prints even numbers from 2 to 10

for i=2 to 10 step 2. print(i). next i

Write a FOR loop in OCR ERL that counts down from 10 to 1

for i=10 to 1 step -1. print(i). next i

Write a WHILE loop in OCR ERL that keeps asking for a password until the user enters "letmein"

password = input("Enter password"). while password != "letmein". password = input("Enter password"). endwhile

Write a DO UNTIL loop in OCR ERL that keeps asking for a number until the user enters a number greater than 10

do. num = int(input("Enter a number")). until num > 10

What are the comparison operators in OCR ERL and what do they mean?

== equal to. != not equal to. < less than.

What are the arithmetic operators in OCR ERL?

• addition. - subtraction. * multiplication. / division. ^ exponentiation (to the power). MOD modulo (remainder after division). DIV quotient (whole number result of division)

What does MOD do and give an example?

Returns the remainder after division — 10 MOD 3 = 1 because 10 divided by 3 is 3 remainder 1 — useful for checking if a number is even or odd

What does DIV do and give an example?

Returns the whole number quotient after division ignoring the remainder — 10 DIV 3 = 3 because 3 goes into 10 three times — useful when you need integer division

What does ^ do and give an example?

Raises a number to a power — 2^3 = 8 because 2 to the power of 3 is 2×2×2 = 8

What are the Boolean operators AND OR and NOT?

AND — both conditions must be true for the overall result to be true. OR — at least one condition must be true. NOT — reverses the Boolean value — NOT true = false

Write an IF statement in OCR ERL that prints "pass" if score >= 50 and "fail" otherwise

if score >= 50 then. print("pass"). else. print("fail"). endif

Write an IF ELSEIF ELSE statement in OCR ERL that grades a score

if score >= 70 then. print("Distinction"). elseif score >= 50 then. print("Pass"). else. print("Fail"). endif

Write a SWITCH CASE statement in OCR ERL for days of the week

switch day :. case "Mon": print("Monday"). case "Tue": print("Tuesday"). default: print("Other day"). endswitch

When would you use SWITCH CASE instead of IF ELSEIF?

When checking a single variable against many possible specific values — SWITCH CASE is cleaner and easier to read than many ELSEIF statements

What is nesting and give an example?

Placing one construct inside another — eg an IF statement inside a FOR loop — for i=1 to 10. if i MOD 2 == 0 then. print(i). endif. next i — this prints even numbers from 1 to 10

Write a nested loop in OCR ERL that prints a 3x3 grid of asterisks

for row=1 to 3. for col=1 to 3. print("*"). next col. next row

What is an integer data type?

Stores whole numbers with no decimal point — eg 5 — 42 — -7 — used for counting discrete items like scores or ages

What is a real data type?

Stores numbers with a decimal point — eg 3.14 — 2.5 — -0.7 — used when precision beyond whole numbers is needed like prices or measurements

What is a Boolean data type?

Can only hold one of two values — True or False — used in conditions and logical operations

What is a character data type?

Stores a single character — eg 'A' — '3' — '!' — enclosed in single quotes

What is a string data type?

Stores a sequence of characters — eg "Hello" — "Computer Science" — enclosed in double quotes — strings can be manipulated using string operations

What is casting?

Temporarily converting a value from one data type to another — useful when combining different data types or performing operations that require a specific type

Give examples of casting functions in OCR ERL

str(345) — converts integer to string. int("3") — converts string to integer. float("4.52") or real("4.52") — converts string to real. bool("True") — converts string to Boolean

Why would you need to cast user input to an integer?

User input is always received as a string — if you want to perform arithmetic on the input you must cast it to an integer first — eg int(input("Enter a number"))

What happens if you try to add a string and an integer without casting?

A type error occurs — the program crashes because you cannot perform arithmetic between incompatible data types

Choose an appropriate data type for storing a person's age

Integer — age is a whole number

Choose an appropriate data type for storing a person's name

String — a name is a sequence of characters

Choose an appropriate data type for storing whether a user is logged in

Boolean — the answer is either True or False

Choose an appropriate data type for storing a product price

Real — prices include decimal values

Choose an appropriate data type for storing a student's grade letter

Character — a single letter like A B or C

2.2 ADDITIONAL PROGRAMMING TECHNIQUES

What is string concatenation?

Joining two or more strings together using the + operator — eg "Hello" + " " + "World" gives "Hello World"

Write OCR ERL code that asks for a first name and last name and prints the full name

firstName = input("First name"). lastName = input("Last name"). print(firstName + " " + lastName)

What does .length do in OCR ERL?

Returns the number of characters in a string — eg subject = "ComputerScience". subject.length returns 15

What does .substring(x,i) do in OCR ERL?

Returns a substring starting at index x with i characters — 0 indexed — eg "ComputerScience".substring(3,5) returns "puter"

What does .left(i) do in OCR ERL?

Returns the first i characters from the left of a string — eg "ComputerScience".left(4) returns "Comp"

What does .right(i) do in OCR ERL?

Returns the last i characters from the right of a string — eg "ComputerScience".right(3) returns "nce"

What does .upper do in OCR ERL?

Converts all characters in a string to uppercase — eg "hello".upper returns "HELLO"

What does .lower do in OCR ERL?

Converts all characters in a string to lowercase — eg "HELLO".lower returns "hello"

What does ASC() do and give an example?

Returns the ASCII numerical value of a character — eg ASC('A') returns 65 — ASC('B') returns 66

What does CHR() do and give an example?

Returns the character corresponding to an ASCII value — eg CHR(65) returns 'A' — CHR(97) returns 'a'

What is a 1D array?

A fixed length list of elements all of the same data type — accessed using a single index — 0 indexed in OCR ERL — like a single row of boxes each with a numbered position

Declare a 1D array called scores with 6 elements in OCR ERL

array scores[6]

Declare a 1D array in OCR ERL with values already assigned

array colours = ["Blue","Pink","Green","Yellow","Red"]

How do you access the third element of an array called names in OCR ERL?

names[2] — because arrays are 0 indexed so the third element is at index 2

How do you assign a value to the first element of an array called scores?

scores[0] = 100

What is a 2D array?

An array with rows and columns — like a grid or table — accessed using two indices — eg gameboard[row,col] — useful for representing grids boards or database tables

Declare a 2D array called gameboard with 8 rows and 8 columns in OCR ERL

array gameboard[8,8]

Assign the value "Pawn" to row 1 column 0 of a 2D array called gameboard

gameboard[1,0] = "Pawn"

Write OCR ERL code to print all elements of a 1D array called scores with 5 elements

for i=0 to 4. print(scores[i]). next i

What are the file handling operations in OCR ERL?

open() — opens a file. .close() — closes a file. .readLine() — reads the next line. .writeLine(text) — writes a line to end of file. .endOfFile() — returns true if end of file reached. newFile() — creates a new file

Write OCR ERL code to open a file read every line and print it

myFile = open("data.txt"). while NOT myFile.endOfFile(). print(myFile.readLine()). endwhile. myFile.close()

Write OCR ERL code to open a file and write a line to it

myFile = open("data.txt"). myFile.writeLine("New line of text"). myFile.close()

What is a record in programming?

A data structure that stores a collection of related fields which can be different data types — similar to a row in a database table — used to represent real-world entities

What is SQL used for in programming?

Structured Query Language — used to search for and retrieve data from a database — can filter and select specific records

What are the three SQL commands you need to know?

SELECT — specifies which fields to retrieve. FROM — specifies which table to retrieve from. WHERE — filters records based on a condition

Write a SQL query to select all students from a table called Students where grade equals "A"

SELECT * FROM Students WHERE grade == "A"

Write a SQL query to select just the name field from a table called Customers where age is greater than 18

SELECT name FROM Customers WHERE age > 18

What is a procedure in programming?

A named block of code that performs a specific task — can accept parameters — does not return a value — called by its name

Write a procedure in OCR ERL that prints a greeting with a name parameter

procedure greet(name). print("Hello " + name). endprocedure

How do you call a procedure in OCR ERL?

greet("Sam") — write the procedure name followed by any parameters in brackets

What is a function in programming?

A named block of code that performs a task and returns a value — can accept parameters — the returned value can be stored or used directly

Write a function in OCR ERL that squares a number and returns the result

function squared(number). squared = number^2. return squared. endfunction

How do you call a function in OCR ERL and use its return value?

result = squared(4) — stores the returned value in a variable. Or print(squared(4)) — uses the returned value directly

What is the difference between a procedure and a function?

A procedure performs a task but does not return a value. A function performs a task and returns a value that can be used elsewhere in the program

What is a local variable?

A variable declared inside a subprogram — only accessible within that subprogram — cannot be used outside it — destroyed when the subprogram ends

What is a global variable?

A variable declared outside all subprograms — accessible from anywhere in the program — declared using the global keyword in OCR ERL

When should you use local variables instead of global variables?

Local variables are preferred — they prevent accidental changes from other parts of the program — make code easier to debug and maintain — global variables should only be used when the variable genuinely needs to be accessed throughout the entire program

How do you generate a random integer between 1 and 6 in OCR ERL?

myVariable = random(1,6)

How do you generate a random real number between 0.0 and 1.0 in OCR ERL?

myVariable = random(0.0,1.0)

Write OCR ERL code that simulates rolling a dice and prints the result

result = random(1,6). print("You rolled: " + str(result))