Lesson 6 - Loops

Loops in Python

For Loop

For Loop is used to repeat a block of code multiple times. It goes through a sequence (like numbers, strings, or lists) one by one.

# Print each letter
for letter in "HELLO":
print(letter)

# Print numbers 1 to 5
for i in [1, 2, 3, 4, 5]:
print(i)

# Loop through list
fruits = ["apple", "banana", "cherry"]
for f in fruits:
print(f)

For Loops with Conditions

You can combine for loops with if statements to make them more powerful.

# Print only even numbers
for i in range(1, 11):
if i % 2 == 0:
print(i)

# Multiplication table of 2
for i in range(1, 6):
print("2 x", i, "=", 2*i)

# Nested loop
for x in range(3):
for y in range(3):
print(x, y)

Tip: range(n) generates numbers from 0 up to n-1. You can also use range(start, end) or range(start, end, step).

# Result will be: 0 1 2
for x in range(3):
print(x)

# Result will be: 0 3 6 9
for y in range(0, 10, 3):
print(y)

While Loop

While Loop is used when you want to repeat a block of code as long as a condition is true.

# Example: count from 1 to 5
i = 1
while i <= 4:
print(i)
i = i + 1

# Output
1
2
3
4

⚠️ Be careful! If the condition is always True, the loop will run forever.
Always make sure the loop updates the variable so it can eventually stop.

Break Statementexits the loop early.

i = 1
while i <= 10:
if i == 5:
break
print(i)
i = i + 1

Continue Statementskips the current loop step and goes to the next one.

i = 0
while i < 5:
i = i + 1
if i == 3:
continue
print(i)

Print numbers from 1 to 5

for i in range(1, 6):
print(i)

💡 Change the range to print 1–10.

Print each letter of a word

for letter in "HELLO":
print(letter)

💡 Try changing the word.

Print items in a list

fruits = ["apple", "banana", "cherry"]
for f in fruits:
print(f)

💡 Add another fruit and run again.

Print a multiplication table for 2

for i in range(1, 11):
print("2 x", i, "=", 2*i)

💡 Try table of 5.

Add all numbers 1 to 10

total = 0
for i in range(1, 11):
total = total + i
print(total)

💡 Change to add numbers 1–20.

Print only even numbers between 1 and 20

for i in range(1, 21):
if i % 2 == 0:
print(i)

💡 Can you make it print odd numbers instead?

Sum numbers until 0 is entered

total = 0
num = int(input("Enter a number (0 to stop): "))

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

print("Total:", total)

👉 Try different numbers.

Print a square of stars ⭐

for i in range(5):
print("*****")

💡 Change it to make a rectangle.

Try nested loop

for i in range(5):
  starRow = ""
  for x in range(4):
    starRow += "*"
  print(starRow)

Cooking recipe

# Muffin Recipe using a list
ingredients = ["flour", "sugar", "eggs", "milk", "butter"]

print("Let's make muffins!")
print("We need:")

for item in ingredients:
print("- " + item)

print("Mix everything together and bake! 🎂")

💡 Try your favorite food recipe

Guess the secret number

secret = 7
guess = 0

while guess != secret:
guess = int(input("Guess the number: "))

print("Correct! 🎉")

👉 Change the secret number.

Use break to stop the loop

i = 1
while i <= 10:
  if i == 5:
    break
  print(i)
  i = i + 1

👉 What numbers will print?

Use continue to skip a number

i = 0
while i < 5:
  i = i + 1
  if i == 3:
    continue
  print(i)

👉 Which number is skipped?

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