Subtopic Notes

8.1 - Programming concepts

8. Programming

Programming is the process of writing instructions in a language a computer can understand to solve problems or perform tasks. It is a transferable skill, meaning the skills developed for one scenario can be easily transferred to another.

Algorithm

Solution to a problem expressed as a sequence of defined steps

Stages of Computer Program

Input: Takes in values from the user to the program
Storage: Temporarily or permanently saves data for use during or after program execution
Process: Operations that transform inputs into outputs
Output: Displays values to the user

Output

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Output

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PSEUDOCODE

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Comments

You may wish to write something in the code which the computer will ignore which is why comments are needed. Text written in a program but not run by the computer is called a comment. These are basically used to explain why a part of code is used, help other people reading the code understand it faster, or Ignore a line of code.

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Output

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PSEUDOCODE

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Variable

Name given to a distinct memory location and contains a value
Can be updated throughout the program

Constant

Name given to a distinct memory location and contains a value
Cannot be updated once it is created
It is good practice to use constants if this makes the pseudocode more readable

Data Types

INTEGER: Represents a whole number
REAL: Represents a floating point number
CHAR: Represents a character, surrounded by single quotes (‘A’)
STRING: Sequence of characters, surrounded by “double quotes”
BOOLEAN: The logical values True or False
ARRAY: A list of same data type
FILE: Resource for recording data in a computer
NULL: No Value

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Output

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PSEUDOCODE

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Identifier

Name given to an entity distinctly identifying an entity in a program
Variable names, function names, class names all are identifiers
It’s a good practice to use PascalCase or camelCase
Rules
- Must be unique
- Cannot have spaces
- Must begin with a letter
- Can consist of letters, digit or underscore
- Reserved words in the language cannot be used (You’ll notice that in pseudocode, keywords are all written in upper-case)
- Names are case sensitive

Input

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Output

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PSEUDOCODE

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Operators

An operator is a symbol or keyword in programming that tells the computer to perform a specific operation on one or more values (called operands)
May be used to compare types REAL/FLOAT and INTEGER
May be used to compare types CHAR and STRING
Case sensitive when used to compare types CHAR and/or STRING
Cannot be used to compare two records or object

Arithmetic operators

Operator	Name	Description	Python	Pseudocode
`+`	Addition	Adds together two values	`a + b`	`a + b`
`-`	Subtraction	Subtracts one value from another	`a - b`	`a - b`
`*`	Multiplication	Multiplies two values	`a * b`	`a * b`
`/`	Division	Divides one value by another	`a / y`	`a / y`
`%`	Modulus	Returns the division remainder	`a % y`	`MOD(a, b)`
`**`	Exponent	Returns a to the power of b	`a ** b`	`^`
`/ /`	Floor Divide	Divide & return the whole number	`a // b`	`DIV(a, b)`

Assignment operators

Operator	Example	Pseudocode
`=`	`a = 5`	`a ← 5`
`<operator>=`	`a += 5` (Represents `a = a + 5`)	Not supported

Comparison operators

Returns a boolean value

Python	Pseudocode	Description
`var == var`	`=`	Equal to
`var != var`	`<>`	Not Equal
`<, >, <=, >=`	`<, >, <=, >=`	Greater/Less than (or equal to)

Logical operators

Works similar to logic gates

Operator	Name	Pseudocode	Example (Pseudocode)
`and`	Logical and	`AND`	`a > 9 AND a < 25`
`or`	Logical or	`OR`	`a > 9 OR a <25`
`not`	Logical Not	`NOT`	`NOT (a = 25)`

Precedence

Sets the rule on the order of operators

Operator	Name
`()`	Parentheses
`**`	Exponent
`* / // %`	Multiplication, Division, Floor Division, Modulus
`+ -`	Addition, Subtraction
`== != > < <= >=`	Comparison Operators
`not`	Logical NOT
`and`	Logical AND
`or`	Logical OR

Conditional/Selection Statements

Allows a program to make decisions and execute different blocks of code based on certain conditions
Selects specific paths depending on the evaluation of boolean expressions

IF Statements

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Output

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PSEUDOCODE

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Indentation: Lines are indented (usually by three spaces) to indicate that they are contained within a statement in a previous line. Notice how in the condition statements, after the conditions are given, there are some blank spaces

Else Statements

Executes one block if the condition is true, another if it's false.

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PSEUDOCODE

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Elif Statements

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Output

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PSEUDOCODE

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Nested If

The same program like above is now being done with nested if statements

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Output

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Pass Statement (Do Nothing)

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Output

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Logical Operators

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Output

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CASE Statements

The match-case statement gives a more readable and efficient way to handle multiple conditions

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Output

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PSEUDOCODE

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Iteration/Loops

Iteration is used when you want to execute a block of code repeatedly. The code is repeated for a specified number of times or until a condition is met.

Count-Controlled Iteration

The code is repeated a fixed number of times. You should use it when you know exactly how many times a block will loop. It clearly expresses the variable initialization, condition and increment in one line (Best for incrementing through an array).

range(start, stop, step)

start (optional):
- Starting value of the sequence.
- Inclusive
- Default Value 0
stop (required):
- The endpoint of the sequence
- Exclusive
step (optional):
- The difference between each number in the sequence
- Defaults Value: 1

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Output

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PSEUDOCODE

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Pre-Conditioned Loops

The condition is checked before each iteration
The loop executes only if the condition is true.
May execute zero times if the condition is false initially
Useful for indefinite loops or when the condition may initially be false

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Output

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PSEUDOCODE

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Post-Conditioned Loops

Condition is checked after the block of code executes
Executes at least once regardless of the condition
Not available in python

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Infinite Loops: A loop that continues to execute endlessly because its termination condition is never met or there is no condition to stop it. It might cause the program to freeze so always make sure to change values of variables when needed. Some infinite loops might be intentional (eg. waiting for an input)

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Output

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Nested Statements

Different types of constructs can be placed one inside another using indentation
It helps to minimize code duplication and makes testing easier

Subroutine

Subroutine is a reusable block of code that is given a name
Designed to perform a specific task
Often called within a program to avoid repetition.
Can be tested/improved independently of program
Easy to share procedures/functions with other programs
Create routines that can be called like built-in command
Header: The first statement in subroutine definition
- Includes name of the subroutine
- Includes parameter passed along with data type
- Includes return data type if it exists

Procedure

Subroutine that does not return a value
Procedure calls are standalone statements

Function

Subroutine that returns a value.
Function calls are always made as part of an expression
The keyword RETURN is used as one of the statements within the body of the function to specify the value to be returned.
Normally, this will be the last statement in the function definition, however, if the RETURN statement is in the body of the function its execution is immediate and any subsequent lines of code are omitted.
Because a function returns a value that is used when the function is called, function calls are not complete program statements
When the RETURN statement is executed, the value returned replaces the function call in the expression and the expression is then evaluated

Parameter

Variables used in a subroutine to accept input values, allowing data to be passed into the subroutine.
A subroutine may or may not have parameters.
When calling a function, the parameters used must be of correct data type and of the same sequence as the definition

Argument: The actual value or data passed to the subroutine when it is called

Local Variable: Variables defined within a function or block, accessible only within that specific scope. These variables are not accessible outside the subroutine

Global Variable: Variables defined outside all functions or blocks, accessible throughout the entire program.

Procedure/Function Interface: The way a procedure or function interacts with the rest of the program. It includes its name, parameters (inputs), and, for functions, the return value.

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Output

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PSEUDOCODE

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Library Routines

A library routine is a pre-written, reusable function or procedure provided by a programming library to perform common tasks, such as mathematical operations or input/output handling.
IDEs typically include a standard library of functions and procedures
Programming language development systems often offer library routines that can be easily integrated into programs
Some examples of library routines in pseudocode are: MOD, DIV, ROUND, RANDOM

Best Coding Practices

Use meaningful identifiers name for variables, constants, arrays, procedure, functions
Use commenting feature wisely
Divide the program into different modules using procedures and functions

String Manipulation

Strings are conceptually like arrays of characters. This means many operations done in arrays can be done in string. It is not zero indexed.

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Slicing/Substring: Returns a range of characters by specifying a start and end index (exclusive)
Concatenation: Combining two or more strings together

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Output

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PSEUDOCODE

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Pseudocode String Functions

An error will be generated if a function call is not properly formed or if the parameters are of an incorrect type or an incorrect value.

String and character functions

A string of length 1 may be considered to be either of type CHAR or STRING
A CHAR may be assigned to, or concatenated with, a STRING
These functions are not zero-indexed

Common string/character functions
`LENGTH(<identifier>)` Returns the integer value representing the length of string. The identifier should be of data type string.
`SUBSTRING(<identifier>, <start>, <length>)` Returns a string of length length starting at position start. The identifier should be of data type string, length and start should be positive and data type integer.
`LCASE(<identifier>)` Returns the string/character with all characters in lower case. The identifier should be of data type string or char.
`UCASE(<identifier>)` Returns the string/character with all characters in upper case. The identifier should be of data type string or char.
In pseudocode, the operator `,` is used to concatenate (join) two strings. Example: `"Summer" , "" , "Pudding"` produces `"Summer Pudding"`

Numeric Functions

Pseudocode Numeric Function
`ROUND(<identifier>, <places>)` Returns the value of the identifier rounded to places number of decimal places. The identifier should be of data type real; places should be data type integer.
`RANDOM()` Returns a random number between 0 and 1 inclusive.
`DIV(<identifier1>, <identifier2>)` Returns the quotient of identifier1 divided by identifier2 with the fractional part discarded. Identifier data type is integer.
`MOD(<identifier1>, <identifier2>)` Returns the remainder of identifier1 divided by identifier2. Identifier data type is integer.
Example `Value ← ROUND (RANDOM() * 6, 0)` Returns a whole number between 0 and 6

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