🐍 Coding & Apps

Algorithms & Python Basics

⏱ 4 hr3 topicsInteractive
🎯 By the end: You can write an algorithm, use Python variables, data types and operators, read input with typecasting, and make decisions with if/elif/else.

Before code comes a plan. Then we write it in Python — a simple, readable language. You can run real Python right here: edit the examples and press Run.

1Algorithms, flowcharts & Python

To solve a problem on a computer, first plan the steps:

  • An algorithm is a step-by-step list of instructions in plain language.
  • A flowchart is a diagram of those steps using standard shapes (oval = start/end, parallelogram = input/output, rectangle = process, diamond = decision).
Algorithm to add two numbers:
1. Start
2. Read a and b
3. sum = a + b
4. Display sum
5. Stop

Python: IDLE & modes

You write Python in IDLE (or any editor). Two ways to run it:

  • Interactive mode — type one line, get the result instantly (good for trying things).
  • Script mode — write a whole program in a .py file and run it all at once.
Key points
  • An algorithm is step-by-step instructions in plain language; a flowchart is their diagram (oval, parallelogram, rectangle, diamond shapes).
  • Python is written in IDLE (or any editor).
  • Interactive mode runs one line at a time; script mode runs a whole .py file.

2Variables, data types & operators

A variable stores a value; its data type says what kind:

TypeExample
int (whole)25
float (decimal)3.14
string (text)"Vidaara"

Operators: arithmetic + - * /, plus // (whole-number divide), % (remainder), ** (power); and = to assign. Run and edit:

Variables & arithmetic▶ runs real Python
main.py
Output
Click Run to execute.
Key points
  • Data types: int (whole), float (decimal), string (text in quotes).
  • Arithmetic: + - * / , and // (whole-number divide), % (remainder), ** (power).
  • = assigns a value to a variable, e.g. total = price * qty.

3Input, typecasting & decisions

input() reads text from the user. Because it always returns a string, you typecast it to a number with int() or float():

name = input("Your name: ")        # a string
age  = int(input("Your age: "))    # typecast to int
print(name, "is", age, "years old")

Making decisions

Use if, if-else and if-elif-else (note the colon and indentation). Run this:

Decisions with if/elif/else▶ runs real Python
main.py
Output
Click Run to execute.
Key points
  • input() reads text (always a string); typecast with int() or float() to do maths.
  • Decisions use if, if-else, and if-elif-else.
  • Python uses a colon (:) and indentation to mark each block — not braces.

★ Practical: small programs

Using the Python playgrounds:

  1. Print your name and class on two lines.
  2. Make two number variables and print their sum, product and remainder.
  3. Change the 'marks' value and re-run to see different grades print.
  4. Write the algorithm (in plain steps) for checking if a number is even or odd.

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