Sum of Digits of a number in python

In this post, we will learn how to write a python program to find the Sum of digits of a given number with its algorithm and explanation in detail.

So let’s start with the algorithm.

Algorithm for Sum of Digits of a number

1.	Take integer input from the User and store it in a variable called “num“
2.	Take one variable to store the sum of digits and initially, it is zero (sum_of_digit = 0).
3.	while num != 0 do —->sum_of_digit += num % 10 —->num = num // 10
4.	Exit from the loop and print(sum_of_digit)

From the above algorithm, we understood how to implement a python program to find the sum of digits of a number but before jumping into the programming part few programming concepts you have to know:

1. Python operators
2. how to take user input
3. while-loop

Source Code

num = int(input('Enter a number: '))
sum_of_digits = 0

while num != 0:
    sum_of_digits += num % 10
    num = num//10

print(f"Sum of Digits of a given number is {sum_of_digits}")

Output

Enter a number: 56
Sum of Digits of a given number is 11

Now let’s modify the above program and write it using a user-defined function.

Sum of Digits of a number in python Using Function

But before writing this program you should know about:

1. Python operators
2. how to take user input
3. while-loop
4. Python Functions

Source Code

def sum_of_digit(n):
    total = 0

    while n != 0:
        total += n % 10
        n = n // 10

    return total

num = int(input('Enter a number: '))
print(f"Sum of Digits of a given number is {sum_of_digit(num)}")

Output

Enter a number: 78
Sum of Digits of a given number is 15

Sum of Digits of a number in python Using for-loop

There is one pythonic way to write this program in which we use the for-loop, str(), and int() functions. So let’s write this program using the pythonic approach and see the output.

But before writing this program you should know about:

1. Python operators
2. how to take user input
3. for-loop

Source Code

num = input('Enter a number : ')
# by default input() function take input in string 
# that's why there is no need to convert into string using str() function
# but if you want to write directly without taking input from user
# then this is the step 
# num = 25
# num = str(num)

sum_of_digits = 0

for i in num:
    sum_of_digits += int(i)

print(f"Sum of Digits of a given number is {sum_of_digits}")

Output

Enter a number : 25
Sum of Digits of a given number is 7