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Sabin Sim
Sabin Sim

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Python basics - Day 07

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Day 7 – While Loop + Mini Projects

Project: Build an Interactive Number Game & Calculator

01. Learning Goal

By the end of this lesson, you will be able to:

  • Use while loops to repeat tasks based on conditions
  • Understand infinite loops, break, and continue
  • Compare for and while loops
  • Build interactive console programs (number guessing, calculator, etc.)

02. Problem Scenario

You want your program to keep running until a condition changes — for example,

asking users for passwords, summing numbers, or repeating actions until the correct answer is given.

The while loop helps make your program more dynamic and interactive.

03. Step 1 – Basic While Loop Structure

A while loop runs as long as its condition is True.

When the condition becomes False, the loop ends.

count = 1

while count <= 5:
    print("Hello", count)
    count += 1
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Output:

Hello 1
Hello 2
Hello 3
Hello 4
Hello 5
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04. Step 2 – Infinite Loop & break

A loop with while True runs forever unless stopped with break.

while True:
    cmd = input("Type 'q' to quit: ")
    if cmd == "q":
        print("Program terminated!")
        break
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05. Step 3 – continue Statement

continue skips the rest of the loop and goes back to the next iteration.

num = 0

while num < 10:
    num += 1
    if num % 2 == 0:
        continue
    print(num)  # Prints only odd numbers
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06. Step 4 – for vs while

  • for loop: When you know how many times to repeat.
  • while loop: When repetition depends on a condition.
Loop Type When to Use Example
for Fixed number of repetitions Iterating through a list
while Conditional repetition Waiting for user input

07. Step 5 – Practice Examples

Example 1: Print Numbers from 1 to 10

n = 1
while n <= 10:
    print(n)
    n += 1
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Example 2: Password Checker

password = "1234"

while True:
    guess = input("Enter password: ")
    if guess == password:
        print("Login successful!")
        break
    else:
        print("Incorrect password. Try again.")
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08. Step 6 – Mini Projects

(1) Multiplication Table (구구단 출력기)

dan = int(input("Enter a number: "))
i = 1

while i <= 9:
    print(f"{dan} x {i} = {dan * i}")
    i += 1
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(2) Sum Calculator

Keep accepting numbers until the user enters 0,
then print the total sum.

total = 0

while True:
    num = int(input("Enter a number (0 to stop): "))
    if num == 0:
        break
    total += num

print("Total Sum:", total)
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(3) Number Guessing Game

import random

secret = random.randint(1, 20)
tries = 0

while True:
    guess = int(input("Guess the number (1–20): "))
    tries += 1
    if guess == secret:
        print(f"Correct! You guessed it in {tries} tries.")
        break
    elif guess < secret:
        print("Try a higher number.")
    else:
        print("Try a lower number.")
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09. Reflection

You have learned how to:

  • Use while loops for dynamic repetition
  • Break out of infinite loops with break
  • Skip specific iterations with continue
  • Build interactive projects such as a password system, calculator, and guessing game

Next → Day 8 – Lists (List Operations)
Learn how to store, modify, and loop through multiple values efficiently.

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