Sum, Count, and Reverse of Digits in Python (While Loop & Recursion)

Source: Dev.to

Sum of digits

Iterative Approach (Using While Loop)

no = int(input("Enter No: "))
sum = 0

while no > 0:
    sum = sum + no % 10
    no = no // 10
else:
    print(sum)

Recursive Approach

def sum_of_digits(no):
    if no == 0:   # Base condition
        return 0
    return (no % 10) + sum_of_digits(no // 10)

no = int(input("Enter No: "))
result = sum_of_digits(no)
print(result)

Count of digits

Iterative Approach (Using While Loop)

num = int(input("Enter number: "))
count = 0

while num > 0:
    num = num // 10
    count += 1

print("Count =", count)

Recursive Approach

def count_digits(num):
    if num == 0:   # base condition
        return 0
    return 1 + count_digits(num // 10)

num = int(input("Enter number: "))

# handle edge case when input is 0
if num == 0:
    print("Count = 1")
else:
    print("Count =", count_digits(num))

Reverse a Number

Iterative Approach (Using While Loop)

num = int(input("Enter number: "))
rev = 0

while num > 0:
    rev = rev * 10 + num % 10
    num = num // 10

print("Reverse =", rev)

Recursive Approach

def reverse_number(num, rev=0):
    if num == 0:   # base condition
        return rev
    return reverse_number(num // 10, rev * 10 + num % 10)

num = int(input("Enter number: "))
result = reverse_number(num)
print("Reverse =", result)