Computer Science Basics — School-Level Programming with Python

This guide introduces programming for school students (Class 9-12, CBSE/ICSE). Python is the ideal first language — readable, powerful, and the same language used by Google, Instagram, and data scientists worldwide.

Why Learn Programming?

Programming is the new literacy. It trains logical thinking, problem-solving, and creativity. Whether you become a doctor, artist, or engineer — the ability to automate tasks, analyse data, and build tools will be valuable.

Python Basics

Your First Program

python

print("Hello, World!")
print("My name is:", "Priya")
print(2 + 3)           # Output: 5
print("Python" * 3)    # Output: PythonPythonPython

Variables and Data Types

python

# Variables store data
name = "Rahul"          # String (text)
age = 16                # Integer (whole number)
height = 5.8            # Float (decimal number)
is_student = True       # Boolean (True or False)

# Check the type
print(type(name))       # <class 'str'>
print(type(age))        # <class 'int'>

# String operations
first = "Hello"
second = "World"
print(first + " " + second)    # Hello World
print(len("Python"))           # 6
print("PYTHON".lower())        # python
print("  spaces  ".strip())    # spaces

# Number operations
print(10 / 3)    # 3.3333 (float division)
print(10 // 3)   # 3 (floor division)
print(10 % 3)    # 1 (remainder/modulus)
print(2 ** 10)   # 1024 (power)

Input from User

python

name = input("Enter your name: ")
age = int(input("Enter your age: "))  # Convert string to integer

print("Hello,", name)
print("You will be", age + 1, "next year")

Conditions — Making Decisions

python

marks = int(input("Enter your marks: "))

if marks >= 90:
    print("Grade A — Excellent!")
elif marks >= 75:
    print("Grade B — Good")
elif marks >= 60:
    print("Grade C — Average")
elif marks >= 35:
    print("Grade D — Pass")
else:
    print("Fail — Please work harder")

# Short form for simple conditions
status = "Adult" if age >= 18 else "Minor"

Loops — Repeating Tasks

python

# for loop — repeat a fixed number of times
for i in range(1, 6):
    print(i, end=" ")  # Output: 1 2 3 4 5

# Print multiplication table
n = int(input("Enter number: "))
for i in range(1, 11):
    print(f"{n} × {i} = {n * i}")

# while loop — repeat while condition is true
count = 1
while count <= 5:
    print(count)
    count = count + 1

# Loop with list
fruits = ["apple", "banana", "mango", "grapes"]
for fruit in fruits:
    print(fruit.upper())

Lists — Storing Multiple Items

python

marks = [85, 92, 78, 96, 88]

print(marks[0])         # 85 (first element)
print(marks[-1])        # 88 (last element)
print(marks[1:3])       # [92, 78] (slicing)

marks.append(95)        # Add to end
marks.insert(0, 99)     # Insert at position
marks.remove(78)        # Remove value
sorted_marks = sorted(marks)  # Sort

# Useful functions
print(len(marks))       # Length
print(sum(marks))       # Sum
print(max(marks))       # Maximum
print(min(marks))       # Minimum

# List comprehension (elegant way to create lists)
squares = [x**2 for x in range(1, 11)]
print(squares)  # [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

even = [x for x in range(1, 21) if x % 2 == 0]
print(even)  # [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]

Functions — Reusable Code Blocks

python

def greet(name, greeting="Hello"):
    """Greet a person with a message."""
    print(f"{greeting}, {name}!")

greet("Priya")           # Hello, Priya!
greet("Raj", "Good morning")  # Good morning, Raj!

def calculate_bmi(weight, height):
    """Calculate BMI given weight (kg) and height (m)."""
    bmi = weight / (height ** 2)
    if bmi < 18.5:
        category = "Underweight"
    elif bmi < 25:
        category = "Normal"
    elif bmi < 30:
        category = "Overweight"
    else:
        category = "Obese"
    return round(bmi, 2), category

bmi, category = calculate_bmi(60, 1.65)
print(f"BMI: {bmi} — {category}")

Common School Programs (Practice These)

python

# 1. Fibonacci Series
def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        print(a, end=" ")
        a, b = b, a + b

fibonacci(10)  # 0 1 1 2 3 5 8 13 21 34

# 2. Prime number check
def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(n**0.5) + 1):
        if n % i == 0:
            return False
    return True

for num in range(2, 50):
    if is_prime(num):
        print(num, end=" ")

# 3. Reverse a string
def reverse_string(s):
    return s[::-1]

print(reverse_string("Python"))  # nohtyP

# 4. Count vowels
def count_vowels(text):
    return sum(1 for char in text.lower() if char in "aeiou")

print(count_vowels("Hello World"))  # 3

# 5. Simple calculator
def calculator(a, op, b):
    operations = {"+": a+b, "-": a-b, "*": a*b, "/": a/b if b!=0 else "Error"}
    return operations.get(op, "Invalid operator")

File Handling (CBSE Class 12 Syllabus)

python

# Writing to a file
with open("students.txt", "w") as f:
    f.write("Name, Marks\n")
    f.write("Priya, 95\n")
    f.write("Raj, 88\n")

# Reading from a file
with open("students.txt", "r") as f:
    content = f.read()
    print(content)

# Reading line by line
with open("students.txt", "r") as f:
    for line in f:
        print(line.strip())

# CSV files (common in data science)
import csv
with open("data.csv", "r") as f:
    reader = csv.DictReader(f)
    for row in reader:
        print(row["Name"], row["Marks"])

What to Learn Next

After mastering these basics:

1. Object-Oriented Programming (OOP)
   Classes, objects, inheritance — organise large programs

2. Data Structures
   Lists, tuples, dictionaries, sets in depth
   
3. Modules and Libraries
   NumPy (numbers), Pandas (data), Matplotlib (graphs)
   
4. Problem Solving on Competitive Platforms
   HackerRank, CodeChef, LeetCode — start with Easy problems
   
5. Build Real Projects
   Calculator, quiz game, simple website, data analysis
   
Career paths from here:
   → Software Engineering (web/mobile/systems)
   → Data Science / Machine Learning
   → DevOps / Cloud Engineering
   → Cybersecurity
   → AI Research

Computer Science — Overview