Programming Fundamentals

1. What is programming?

Programming is the process of designing and writing instructions that a computer can execute. A program may perform a calculation, process data, display information, or control a system.

START
  INPUT mark1, mark2, mark3
  average = (mark1 + mark2 + mark3) / 3
  DISPLAY average
END

2. Variables and constants

A variable is a named place used to hold a value that may change while a program runs. A constant represents a value that should remain fixed within the relevant program context.

score = 10
score = score + 5
DISPLAY score

CONSTANT TAX_RATE = 0.05

Rules for naming variables

• Choose descriptive names, such as total_price.
• Follow the naming rules of the language being used.
• Avoid reserved words used by the language.
• Use a consistent naming style.

3. Data types

A data type describes the kind of value a variable can represent and the operations available for it.

Languages differ: some use static type declarations, while others infer or determine types at runtime. Floating-point arithmetic may introduce small rounding errors.

4. Operators

Operators perform calculations, comparisons, or logical operations.

Operator symbols vary across languages. In many languages, = assigns a value, while == compares two values.

5. Input and output

Input brings information into a program. Output communicates a result to the user or another system.

START
  INPUT name
  DISPLAY "Welcome, " + name
END

Real programs should validate input when necessary. For example, a program expecting a number should handle invalid text appropriately.

6. Conditional statements

Conditions let a program choose which instructions to execute based on whether a logical expression is true or false.

INPUT age

IF age >= 18
  DISPLAY "Adult"
ELSE
  DISPLAY "Under 18"
END IF

Multiple conditions

INPUT score

IF score >= 90
  DISPLAY "Grade A"
ELSE IF score >= 75
  DISPLAY "Grade B"
ELSE IF score >= 50
  DISPLAY "Grade C"
ELSE
  DISPLAY "Needs improvement"
END IF

Order matters: the first matching branch is selected. Here, the score ranges are handled from highest to lowest.

7. Loops

Loops repeat a block of instructions. They are useful for processing lists, repeating calculations, and performing tasks until a condition is met.

For loop

FOR i = 1 TO 5
  DISPLAY i
END FOR

Displays the numbers 1 through 5, assuming the inclusive range shown in this pseudocode.

While loop

count = 1

WHILE count <= 3
  DISPLAY count
  count = count + 1
END WHILE

The loop stops when count becomes 4. Updating the variable prevents an endless loop in this example.

8. Functions

A function is a reusable block of code that performs a defined task. Functions can accept inputs called parameters and may return a result.

FUNCTION square(number)
  RETURN number * number
END FUNCTION

result = square(4)
DISPLAY result

Functions help programmers:

• Reuse logic instead of repeating code.
• Break complex problems into smaller tasks.
• Test and maintain parts of a program independently.
• Give meaningful names to operations.

9. Arrays and strings

An array or list can store multiple values in an ordered collection. A string represents text.

numbers = [4, 7, 2, 9]
total = 0

FOR EACH number IN numbers
  total = total + number
END FOR

DISPLAY total

Indexing conventions vary. Many languages begin array indices at 0, while some educational pseudocode and languages use 1.

10. Errors and debugging

Programs may fail or produce incorrect results. Three common error categories are:

A useful debugging process is to reproduce the problem, inspect inputs and intermediate values, identify the cause, make a correction, and test the program again.

11. Quick knowledge check

Try each question before revealing its answer.