Use built-in functions and library routines

Programming Basics – Built‑in Functions & Library Routines (Cambridge IGCSE/A‑Level 9618)

1. Quick‑Reference Overview

• Built‑in functions: Always available, no import required. Used for fundamental I/O, type conversion and simple sequence handling.
• Library routines: Belong to a module (Python) or package (Java). Must be imported before use and are accessed via a namespace.
• Control structures, procedures & functions, exception handling are all required for AO1–AO3.
• Additional AS‑level topics that must be linked to programming:
  • Data‑type declarations, arrays, records, files, ADTs (stack/queue/linked list)
  • Number systems, binary/hexadecimal conversion, bit manipulation
  • Logic‑gate truth tables
  • Security, ethics & privacy
  • Basic hardware/processor concepts

2. Built‑in Functions

These functions are part of the core language and require no import statement.

2.1 Number Systems & Bit Manipulation (AS 1.1 & 4.3)

• Binary (base‑2), Decimal (base‑10) and Hexadecimal (base‑16) are the three systems examined.
• Conversion examples:

  # Decimal → Binary
  bin(13)          # '0b1101'
  
  # Binary → Decimal
  int('1101', 2)   # 13
  
  # Decimal → Hex
  hex(255)         # '0xff'
  
  # Hex → Decimal
  int('FF', 16)    # 255

• Simple bit‑wise operations (required for AS 4.3):

  # Left shift (multiply by 2ⁿ)
  x = 5            # 0b0101
  x << 2           # 0b010100 = 20
  
  # Right shift (integer division by 2ⁿ)
  x >> 1           # 0b0010 = 2
  
  # Bitwise AND, OR, XOR
  a & b            # 0b0100
  a | b            # 0b0111
  a ^ b            # 0b0011

2.2 Logic‑Gate Truth Tables (AS 3.2)

A B | A∧B
0 0 | 0
0 1 | 0
1 0 | 0
1 1 | 1

A B | A∨B
0 0 | 0
0 1 | 1
1 0 | 1
1 1 | 1

A | ¬A
0 | 1
1 | 0

A B | A⊕B
0 0 | 0
0 1 | 1
1 0 | 1
1 1 | 0

3. Library Routines (Modules / Packages)

Library routines live inside a module (Python) or package (Java). They must be imported before use.

3.1 Common Standard‑Library Modules (Python)

• math – advanced mathematics, constants (π, e).
• random – pseudo‑random number generation.
• sys – interpreter parameters, command‑line arguments.
• os – file‑system and OS interaction.
• datetime – dates, times, timedeltas.
• io – low‑level stream handling (open, read, write, close).

3.2 Import Styles

• import math – use as math.sqrt(...)
• from math import sqrt, pi – use directly as sqrt(...)
• import math as m – use as m.sqrt(...)

Exam tip: Avoid import * – it obscures the namespace and can cause name clashes.

3.3 Example: Using math and random

# math – area of a circle
import math
r = 5
area = math.pi * math.pow(r, 2)
print("Area =", area)

# random – roll a die
import random
die = random.randint(1, 6)   # inclusive
print("Die roll:", die)

3.4 File‑handling (Built‑ins + io module)

# Write numbers to a file
with open('numbers.txt', 'w') as f:
    for n in [12, 7, 5]:
        f.write(str(n) + '')

# Read back and compute the mean
total = 0
count = 0
with open('numbers.txt', 'r') as f:
    for line in f:
        total += int(line.strip())
        count += 1
mean = total / count
print('Mean =', mean)

3.5 Exception Handling (Python, Java, Visual Basic)

try:
    f = open('data.txt', 'r')
    data = f.read()
except FileNotFoundError:
    print('File not found – please check the filename.')
finally:
    f.close()

try {
    // code that may throw an exception
} catch (FileNotFoundException e) {
    System.out.println("File not found");
} finally {
    // optional clean‑up code
}

Try
    ' code that may raise an error
Catch ex As IOException
    Console.WriteLine("File not found")
Finally
    ' clean‑up code
End Try

4. Control Structures – Cheat‑Sheet (AO2 & AO3)

4.1 Algorithmic Complexity (AO2)

When choosing a loop or data‑structure, note its time‑complexity:

• Linear scan – O(n) – suitable for small‑to‑medium lists.
• Binary search – O(log n) – requires a sorted array; faster for large data sets.
• Stack/Queue operations – O(1) for push/pop or enqueue/dequeue.

In exam answers, a brief comment such as “linear time, O(n)” earns marks for justification.

5. Structured Programming – Procedures, Functions & ADTs

5.1 Definitions (Cambridge terminology)

• Procedure – performs an action, no return value (returns None in Python).
• Function – computes a value and returns it with return.
• ADT (Abstract Data Type) – a logical description of a data structure (stack, queue, linked list) together with the operations that can be performed on it.

5.2 Python Examples

# Procedure – prints a greeting
def greet(name):
    print("Hello, " + name)

# Function – factorial (recursive)
def factorial(n):
    if n == 0:
        return 1
    return n * factorial(n-1)

# Simple stack ADT using a list
class Stack:
    def __init__(self):
        self._data = []               # private list

    def push(self, item):
        self._data.append(item)

    def pop(self):
        if not self._data:
            raise IndexError("pop from empty stack")
        return self._data.pop()

    def is_empty(self):
        return len(self._data) == 0

5.3 Pseudocode Equivalents

PROCEDURE Greet(name)
    OUTPUT "Hello, " + name
END PROCEDURE

FUNCTION Factorial(n) RETURNS INTEGER
    IF n = 0 THEN
        RETURN 1
    ELSE
        RETURN n * Factorial(n-1)
    END IF
END FUNCTION

TYPE Stack
    data : ARRAY[0..99] OF INTEGER   // simple fixed‑size array
    top  : INTEGER := -1
END TYPE

PROCEDURE Push(s : INOUT Stack, value : INTEGER)
    s.top ← s.top + 1
    s.data[s.top] ← value
END PROCEDURE

FUNCTION Pop(s : INOUT Stack) RETURNS INTEGER
    IF s.top = -1 THEN
        ERROR "Stack underflow"
    END IF
    value ← s.data[s.top]
    s.top ← s.top - 1
    RETURN value
END FUNCTION

5.4 Java / Visual Basic Sketches

public static void greet(String name) {
    System.out.println("Hello, " + name);
}

public static int factorial(int n) {
    if (n == 0) return 1;
    return n * factorial(n-1);
}

public class Stack {
    private int[] data = new int[100];
    private int top = -1;

    public void push(int v) {
        data[++top] = v;
    }

    public int pop() {
        if (top < 0) throw new EmptyStackException();
        return data[top--];
    }

    public boolean isEmpty() {
        return top == -1;
    }
}

Sub Greet(name As String)
    Console.WriteLine("Hello, " & name)
End Sub

Function Factorial(n As Integer) As Integer
    If n = 0 Then
        Return 1
    Else
        Return n * Factorial(n - 1)
    End If
End Function

Structure Stack
    Private data(99) As Integer
    Private top As Integer = -1
End Structure

Sub Push(ByRef s As Stack, ByVal v As Integer)
    s.top += 1
    s.data(s.top) = v
End Sub

Function Pop(ByRef s As Stack) As Integer
    If s.top = -1 Then Throw New InvalidOperationException("underflow")
    Dim v As Integer = s.data(s.top)
    s.top -= 1
    Return v
End Function

5.5 Quick‑Reference: Arrays, Records, Files & ADTs

6. Software Development Life‑Cycle (SDLC) & Testing

6.1 Typical SDLC Models (Cambridge focus)

• Waterfall – sequential: requirements → design → implementation → testing → maintenance.
• Iterative / Incremental – develop a small part, test, then refine.
• Rapid Application Development (RAD) – quick prototype → feedback → improvement.

6.2 Testing Checklist (Paper 4 – programming)

1. Syntax check – code compiles / runs without errors.
2. Logical check – algorithm follows the specification.
3. Boundary testing – test minimum, maximum and typical values.
4. Exception testing – verify handling of error conditions (e.g., file not found, division by zero).
5. Black‑box testing – test against the specification without looking at the code.
6. White‑box testing – examine all code paths, loops and conditionals for full coverage.
7. Complexity justification – note the time‑complexity (O(n), O(log n), etc.) when relevant.

6.3 Security, Ethics & Privacy (AS 7)

7. Basic Hardware & Processor Recap (AS 3.1 & 3.2)

• CPU cycle – Fetch → Decode → Execute → Store.
• Registers – small, fast storage inside the CPU (e.g., accumulator, program counter).
• ALU – performs arithmetic and logical operations (add, subtract, AND, OR, NOT).
• Memory hierarchy – registers → cache → main RAM → secondary storage.
• Parallel processing (A‑level) – multiple cores execute instructions simultaneously; concepts of threads and synchronization are introduced later.

8. Comparison – Built‑in Functions vs. Library Routines

9. Best Practices for Exams (Paper 2 & Paper 4)

1. Prefer built‑in functions for simple tasks – they keep code short and are less error‑prone.
2. Import only the modules you need; avoid import *.
3. Use explicit imports (from math import sqrt, pi) when you need only a few routines.
4. When writing pseudocode, replace Python built‑ins with the Cambridge equivalents shown in the mapping tables.
5. Include basic error handling for I/O and conversion operations (try/except or try/catch).
6. Comment briefly to show logical structure – markers look for clarity.
7. Test with at least three different input sets, including edge cases and invalid data.
8. State the algorithmic complexity where relevant (e.g., “linear scan – O(n)”).
9. Remember security/ethics reminders – a short comment on data validation or confidentiality can earn marks.

10. Typical Exam Questions (Paper 2 & Paper 4)

• Write a program that reads a list of integers, stores them in an array/list, and prints the mean using sum() and len() (built‑ins).
• Explain the difference between math.pow(x, y) and the exponentiation operator x**y. Include a short example.
• Given a scenario that requires random selection of a quiz question, choose an appropriate function from the random module, justify your choice and show the code.
• Design a procedure called saveData that writes a list of strings to a file called output.txt. Show both the Python implementation and the equivalent pseudocode.
• Write a try/except block that attempts to open a file called data.txt. If the file does not exist, output “File not found”. Include a finally clause that closes the file.
• Implement a simple stack ADT with push, pop and isEmpty operations. Provide Python code and the corresponding Cambridge pseudocode.
• Discuss the time‑complexity of scanning an array to find the maximum value versus using a binary search on a sorted array.

11. Key Take‑aways

• Built‑in functions are always available and ideal for fundamental tasks such as I/O, type conversion and simple sequence operations.
• Library routines extend the language; they must be imported and are accessed via a module namespace.
• Control structures, procedures, functions and ADTs are core to structured programming and are examined across AO1–AO3.
• Understanding number systems, bit manipulation and logic gates satisfies the AS‑level hardware and data‑representation requirements.
• Security, ethics and privacy considerations are part of the syllabus – a brief comment in code demonstrates awareness.
• Clear, well‑commented code, appropriate use of built‑ins, and a short justification of algorithmic choices earn maximum marks.