🚀 Day 13/150 – Simple Calculator in Python

Welcome back to the 150 Days of Python series! 🔥
Today, we’ll build a Simple Calculator — one of the most important beginner projects.

This project helps you understand:

• Conditional statements
• Functions
• User input
• Error handling

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🎯 Problem Statement

Create a Python program that performs basic operations:

• Addition ➕
• Subtraction ➖
• Multiplication ✖️
• Division ➗

✅ Method 1 – Using if-elif-else

print("Simple Calculator") a = float(input("Enter first number: ")) b = float(input("Enter second number: ")) operation = input("Enter operation (+, -, *, /): ") if operation == "+": print("Result:", a + b) elif operation == "-": print("Result:", a - b) elif operation == "*": print("Result:", a * b) elif operation == "/": if b != 0: print("Result:", a / b) else: print("Division by zero is not allowed") else: print("Invalid operation")

🔍 Explanation:

input() → takes user input

float() → converts input into numbers

if-elif-else → checks which operation user selected

👉 Important:

Always check b != 0 before division to avoid errors.

✅ Method 2 – Using Functions

def add(x, y): return x + y def subtract(x, y): return x - y def multiply(x, y): return x * y def divide(x, y): if y != 0: return x / y else: return "Division by zero not allowed" print(add(10, 5)) print(subtract(10, 5)) print(multiply(10, 5)) print(divide(10, 5))

🔍 Why use functions?

Code becomes modular

Easy to reuse

Cleaner structure

👉 This approach is closer to real-world coding.

✅ Method 3 – Using Lambda Functions

add = lambda x, y: x + y subtract = lambda x, y: x - y multiply = lambda x, y: x * y divide = lambda x, y: x / y if y != 0 else "Cannot divide by zero" print(add(10, 5)) print(subtract(10, 5)) print(multiply(10, 5)) print(divide(10, 5))

🔍 Explanation:

lambda → creates small anonymous functions

Useful for short, one-line operations

👉 Best for concise code, but not always readable for beginners.

⚠️ Important Things to Remember

✔ Always convert input (int() or float())
✔ Handle division by zero
✔ Validate user input
✔ Keep code clean and readable

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🧠 Summary

Method	Concept
if-elif-else	Basic logic
Functions	Reusability
Lambda	Short & compact