Solution on Loops

🧮 1. Print Numbers from 1 to 10

Problem:
Print numbers from 1 to 10 using a for loop.

Example Output:

Solution:

for i in range(1, 11):
    print(i)

Explanation:
range(1, 11) generates numbers from 1 to 10.
The for loop prints each number one by one.

🔢 2. Sum of First N Natural Numbers

Problem:
Calculate the sum of numbers from 1 to N.

Example Input:

N = 5

Example Output:

Solution:

N = 5
total = 0
for i in range(1, N + 1):
    total += i
print(total)

Explanation:
We initialize a variable total and keep adding each number in every loop cycle.

⭐ 3. Print Each Character in a String

Problem:
Print each character of a string using a for loop.

Example Input:

Python

Example Output:

P
y
t
h
o
n

Solution:

word = "Python"
for char in word:
    print(char)

Explanation:
Strings are iterable — the loop automatically picks each character one by one.

🧾 4. Print Even Numbers from 1 to 20

Problem:
Print only even numbers between 1 and 20.

Example Output:

2 4 6 8 10 12 14 16 18 20

Solution:

for i in range(2, 21, 2):
    print(i, end=" ")

Explanation:
The third argument in range(start, stop, step) controls the increment.
Here, we step by 2 to get only even numbers.

💬 5. Print List Elements Using Loop

Problem:
Display all elements from a list using a loop.

Example Input:

fruits = ["apple", "banana", "cherry"]

Example Output:

apple
banana
cherry

Solution:

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

Explanation:
Looping over a list gives you each element directly — no index needed.

🔄 6. Reverse Counting from 10 to 1

Problem:
Print numbers from 10 down to 1.

Example Output:

10 9 8 7 6 5 4 3 2 1

Solution:

for i in range(10, 0, -1):
    print(i, end=" ")

Explanation:
Using a negative step value in range() helps count backward.

⏳ 7. Print Multiplication Table of a Number

Problem:
Take a number and print its multiplication table up to 10.

Example Input:

n = 3

Example Output:

3 x 1 = 3
3 x 2 = 6
...
3 x 10 = 30

Solution:

n = 3
for i in range(1, 11):
    print(f"{n} x {i} = {n * i}")

Explanation:
We multiply n by each i in range 1–10 and print the result.

🧠 8. Find the Factorial of a Number

Problem:
Find factorial of a number (e.g., 5! = 1×2×3×4×5).

Example Input:

Example Output:

Solution:

n = 5
fact = 1
for i in range(1, n + 1):
    fact *= i
print(fact)

Explanation:
Multiply all numbers from 1 to n sequentially to find the factorial.

🔁 9. Print Digits of a Number (Using while loop)

Problem:
Display each digit of a number separately.

Example Input:

Example Output:

Solution:

num = 1234
while num > 0:
    digit = num % 10
    print(digit)
    num //= 10

Explanation:
Use modulo % to extract the last digit and integer division // to remove it.

🎮 10. FizzBuzz (Classic Loop Problem)

Problem:
Print numbers 1–20 but:

Print “Fizz” if divisible by 3
Print “Buzz” if divisible by 5
Print “FizzBuzz” if divisible by both

Example Output:

1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz
...

Solution:

for i in range(1, 21):
    if i % 3 == 0 and i % 5 == 0:
        print("FizzBuzz")
    elif i % 3 == 0:
        print("Fizz")
    elif i % 5 == 0:
        print("Buzz")
    else:
        print(i)

Explanation:
Conditions are checked in order.
If both 3 and 5 divide the number, print "FizzBuzz" first — otherwise the correct single case.

🧮 11. Sum of Even Numbers in a List

Problem: Calculate the sum of all even numbers in a given list.
Example Input:

numbers = [1, 4, 7, 10, 12]

Output:

numbers = [1, 4, 7, 10, 12]
total = 0
for num in numbers:
    if num % 2 == 0:
        total += num
print(total)

Explanation: Loop over each number; if divisible by 2, add to total.

🔢 12. Count Vowels in a String

Problem: Count the number of vowels in a string.
Input: "Python is fun"
Output: 4

text = "Python is fun"
vowels = "aeiouAEIOU"
count = 0
for char in text:
    if char in vowels:
        count += 1
print(count)

Explanation: Check each character; increment counter if it’s a vowel.

⭐ 13. Print Numbers Divisible by 4 and 6

Problem: Print numbers from 1 to 50 divisible by both 4 and 6.
Output:

12 24 36 48

for i in range(1, 51):
    if i % 4 == 0 and i % 6 == 0:
        print(i, end=" ")

Explanation: Use modulo operator to check divisibility by both numbers.

🧾 14. Cumulative Sum of List

Problem: Print cumulative sum at each step from a list.
Input: [2, 5, 3, 7]
Output: 2 7 10 17

numbers = [2, 5, 3, 7]
total = 0
for num in numbers:
    total += num
    print(total, end=" ")

Explanation: Add each number to a running total and print progressively.

🔄 15. Print Multiples of 3 and 5

Problem: Print numbers between 1–50 divisible by 3 or 5.
Output:

3 5 6 9 10 12 ... 45 48 50

for i in range(1, 51):
    if i % 3 == 0 or i % 5 == 0:
        print(i, end=" ")

Explanation: Check each number for divisibility by 3 or 5 using %.

⏳ 16. Reverse a String

Problem: Print a string in reverse.
Input: "Python"
Output: nohtyP

text = "Python"
reversed_text = ""
for char in text:
    reversed_text = char + reversed_text
print(reversed_text)

Explanation: Prepend each character to the result string to reverse it.

🧠 17. Find Numbers with Even Digits

Problem: Print numbers from 1–100 that have an even number of digits.
Output:

10 11 12 ... 99

for i in range(1, 101):
    if len(str(i)) % 2 == 0:
        print(i, end=" ")

Explanation: Convert each number to string; check if its length is even.

🔁 18. Find the Maximum Number in a List

Problem: Find the largest number in a list.
Input: [5, 12, 3, 21, 7]
Output: 21

numbers = [5, 12, 3, 21, 7]
max_num = numbers[0]
for num in numbers:
    if num > max_num:
        max_num = num
print(max_num)

Explanation: Compare each element with max_num and update if larger.

🔢 19. Count Digits and Letters in a String

Problem: Count letters and digits separately in a string.
Input: "Python3.8"
Output:

Letters: 6
Digits: 2

text = "Python3.8"
letters = digits = 0
for char in text:
    if char.isalpha():
        letters += 1
    elif char.isdigit():
        digits += 1
print("Letters:", letters)
print("Digits:", digits)

Explanation: Use isalpha() and isdigit() to categorize each character.

🎮 20. Fibonacci Numbers Less Than N

Problem: Print all Fibonacci numbers less than a given N.
Input: N = 20
Output: 0 1 1 2 3 5 8 13

N = 20
a, b = 0, 1
while a < N:
    print(a, end=" ")
    a, b = b, a + b

Explanation: Generate Fibonacci numbers in a while loop until exceeding N.

🧮 21. Print Odd Numbers in a List

Problem: Print all odd numbers from a given list.
Example Input:

numbers = [2, 7, 4, 9, 12, 15]

Output:

7 9 15

numbers = [2, 7, 4, 9, 12, 15]
for num in numbers:
    if num % 2 != 0:
        print(num, end=" ")

Explanation: Check if a number is not divisible by 2 using %.

🔢 22. Count Uppercase and Lowercase Letters

Problem: Count the number of uppercase and lowercase letters in a string.
Input: "Python Is Fun"
Output:

Uppercase: 3
Lowercase: 8

text = "Python Is Fun"
upper = lower = 0
for char in text:
    if char.isupper():
        upper += 1
    elif char.islower():
        lower += 1
print("Uppercase:", upper)
print("Lowercase:", lower)

Explanation: Use isupper() and islower() for classification.

⭐ 23. Print Squares of Numbers

Problem: Print squares of numbers from 1 to N.
Input: N = 5
Output:

1 4 9 16 25

N = 5
for i in range(1, N + 1):
    print(i**2, end=" ")

Explanation: Multiply each number by itself using the exponent operator **.

🧾 24. Print Cubes of Numbers in a List

Problem: Print cubes of numbers from a given list.
Input: [1, 2, 3, 4]
Output:

1 8 27 64

numbers = [1, 2, 3, 4]
for num in numbers:
    print(num**3, end=" ")

Explanation: Use num**3 to calculate the cube of each number.

🔄 25. Print Numbers Divisible by 7 but Not by 5

Problem: Print numbers from 1 to 100 divisible by 7 but not by 5.
Output:

7 14 21 28 ... 91 98

for i in range(1, 101):
    if i % 7 == 0 and i % 5 != 0:
        print(i, end=" ")

Explanation: Use two conditions combined with and and !=.

⏳ 26. Print Factorials of Numbers in a List

Problem: Print factorial of each number in a given list.
Input: [3, 4, 5]
Output:

6 24 120

numbers = [3, 4, 5]
for num in numbers:
    fact = 1
    for i in range(1, num + 1):
        fact *= i
    print(fact, end=" ")

Explanation: Use a loop to calculate the factorial of each number.

🧠 27. Count Words in a Sentence

Problem: Count the number of words in a given sentence.
Input: "Python is fun to learn"
Output: 5

sentence = "Python is fun to learn"
words = 0
for char in sentence:
    if char == " ":
        words += 1
words += 1
print(words)

Explanation: Count spaces between words; add 1 to get total words.

🔁 28. Print Prime Numbers from 1 to N

Problem: Print all prime numbers from 1 to N.
Input: N = 20
Output:

2 3 5 7 11 13 17 19

N = 20
for num in range(2, N + 1):
    is_prime = True
    for i in range(2, num):
        if num % i == 0:
            is_prime = False
            break
    if is_prime:
        print(num, end=" ")

Explanation: A number is prime if it has no divisors other than 1 and itself.

🔢 29. Sum of Digits of Numbers in a List

Problem: Print sum of digits for each number in a list.
Input: [12, 34, 56]
Output:

3 7 11

numbers = [12, 34, 56]
for num in numbers:
    total = 0
    temp = num
    while temp > 0:
        total += temp % 10
        temp //= 10
    print(total, end=" ")

Explanation: Use modulo % to get digits and integer division // to remove them.

🎮 30. Check Palindrome Numbers in a List

Problem: Print all numbers from a list that are palindromes.
Input: [121, 123, 454, 567, 787]
Output:

121 454 787

numbers = [121, 123, 454, 567, 787]
for num in numbers:
    if str(num) == str(num)[::-1]:
        print(num, end=" ")

Explanation: Convert the number to a string and check if it reads the same forward and backward.