Python problems on loops 2 solution

Problem 1: Sum of Natural Numbers

Question: Write a program to find the sum of the first n natural numbers.

• Example Input:n = 5

• Example Output:15

• Solution:

n = 5
sum = 0
for i in range(1, n + 1):
    sum += i
print(sum)

• Explanation: The loop iterates from 1 to n, adding each number to sum.

Problem 2: Factorial of a Number

Question: Write a program to find the factorial of a number n.

• Example Input:n = 4

• Example Output:24

• Solution:

n = 4
factorial = 1
for i in range(1, n + 1):
    factorial *= i
print(factorial)

• Explanation: The loop multiplies factorial by each number from 1 to n.

Problem 3: Print Multiplication Table

Question: Write a program to print the multiplication table of a number n.

• Example Input:n = 3

• Example Output:

  3 x 1 = 3
  3 x 2 = 6
  3 x 3 = 9
  ...
  3 x 10 = 30

• Solution:

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

• Explanation: The loop prints the product of n and each number from 1 to 10.

Problem 4: Reverse a String

Question: Write a program to reverse a given string.

• Example Input:s = "hello"

• Example Output:olleh

• Solution:

s = "hello"
reversed_s = ""
for char in s:
    reversed_s = char + reversed_s
print(reversed_s)

• Explanation: The loop prepends each character of s to reversed_s.

Problem 5: Count Digits in a Number

Question: Write a program to count the number of digits in a number n.

• Example Input:n = 12345

• Example Output:5

• Solution:

n = 12345
count = 0
while n != 0:
    n //= 10
    count += 1
print(count)

• Explanation: The loop divides n by 10 until n becomes 0, counting the divisions.

Problem 6: Fibonacci Sequence

Question: Write a program to print the first n terms of the Fibonacci sequence.

• Example Input:n = 5

• Example Output:0 1 1 2 3

• Solution:

n = 5
a, b = 0, 1
for _ in range(n):
    print(a, end=" ")
    a, b = b, a + b

• Explanation: The loop prints a and updates a and b to the next Fibonacci numbers.

Problem 7: Sum of Digits

Question: Write a program to find the sum of digits of a number n.

• Example Input:n = 123

• Example Output:6

• Solution:

n = 123
sum = 0
while n > 0:
    sum += n % 10
    n //= 10
print(sum)

• Explanation: The loop extracts the last digit of n and adds it to sum.

Problem 8: Palindrome Check

Question: Write a program to check if a given string is a palindrome.

• Example Input:s = "racecar"

• Example Output:True

• Solution:

s = "racecar"
is_palindrome = True
for i in range(len(s) // 2):
    if s[i] != s[-(i + 1)]:
        is_palindrome = False
        break
print(is_palindrome)

• Explanation: The loop compares characters from the start and end of the string.

Problem 9: Find the Largest Number

Question: Write a program to find the largest number in a list.

• Example Input:lst = [3, 1, 4, 1, 5, 9]

• Example Output:9

• Solution:

lst = [3, 1, 4, 1, 5, 9]
largest = lst[0]
for num in lst:
    if num > largest:
        largest = num
print(largest)

• Explanation: The loop updates largest if it finds a larger number in lst.

Problem 10: Find the Second Largest Number

Question: Write a program to find the second largest number in a list.

• Example Input:lst = [3, 1, 4, 1, 5, 9]

• Example Output:5

• Solution:

lst = [3, 1, 4, 1, 5, 9]
largest = second_largest = float('-inf')
for num in lst:
    if num > largest:
        second_largest = largest
        largest = num
    elif num > second_largest and num != largest:
        second_largest = num
print(second_largest)

• Explanation: The loop updates largest and second_largest appropriately.

Problem 11: Count Vowels in a String

Question: Write a program to count the number of vowels in a given string.

• Example Input:s = "hello"

• Example Output:2

• Solution:

s = "hello"
vowels = "aeiou"
count = 0
for char in s:
    if char in vowels:
        count += 1
print(count)

• Explanation: The loop checks if each character is a vowel and increments count.

Problem 12: Sum of Even Numbers

Question: Write a program to find the sum of even numbers from 1 to n.

• Example Input:n = 10

• Example Output:30

• Solution:

n = 10
sum = 0
for i in range(2, n + 1, 2):
    sum += i
print(sum)

• Explanation: The loop iterates over even numbers and adds them to sum.

Problem 13: Count Words in a String

Question: Write a program to count the number of words in a given string.

• Example Input:s = "hello world"

• Example Output:2

• Solution:

s = "hello world"
count = 1
for char in s:
    if char == ' ':
        count += 1
print(count)

• Explanation: The loop counts spaces and adds 1 to get the number of words.