What is 1234 // 10 in Python?

123. The // operator is floor division: it divides and throws away the remainder, so the last digit disappears. 1234 / 10 with a single slash gives 123.4.

What is 1234 % 10 in Python?

4. The % operator gives the remainder, and the remainder after dividing by 10 is always the last digit.

What does n //= 10 mean in Python?

It is short for n = n // 10 — divide n by 10, drop the remainder and store the result back in n. In a digit loop it removes the last digit on every pass until n becomes 0.

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Python Program to Find the Sum of Digits of a Number

easywhile loopPython

The standard way to take a number apart digit by digit — the same technique is used for reverse, palindrome and Armstrong programs.

The question

Read a positive integer and print the sum of its digits. Use a while loop with % 10 and // 10.

The code

program.py

n = int(input())
total = 0
while n > 0:
    total += n % 10
    n //= 10
print("Sum of digits =", total)

Try it Yourself »

Input

Output

Sum of digits = 14

How it works

1n % 10 gives the last digit (1234 % 10 = 4).
2Add that digit to total.
3n //= 10 removes the last digit (1234 becomes 123).
4Repeat while n is greater than 0; when every digit is used, n becomes 0 and the loop ends.

Common mistakes

Using / instead of // — n becomes 123.4 and the loop never works properly.
Forgetting to change n inside the loop, which makes the loop run forever.

Sum of digits using a for loop and a string

Leave the input as text. A for loop over a string gives one character at a time, and int(ch) turns each one into a digit.

program.py

n = input().strip()
total = 0
for ch in n:
    total += int(ch)
print("Sum of digits =", total)

Try it Yourself »

Input

Output

Sum of digits = 10

Questions students ask

What is 1234 // 10 in Python?: 123. The // operator is floor division: it divides and throws away the remainder, so the last digit disappears. 1234 / 10 with a single slash gives 123.4.
What is 1234 % 10 in Python?: 4. The % operator gives the remainder, and the remainder after dividing by 10 is always the last digit.
What does n //= 10 mean in Python?: It is short for n = n // 10 — divide n by 10, drop the remainder and store the result back in n. In a digit loop it removes the last digit on every pass until n becomes 0.

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Practice questions

Preparing for NIELIT O Level?

This program is the kind asked in the M3 (Python) theory paper and the PR-3 practical exam.

More in while loop

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