DSA interview question

For Loops: Multiplication Table and Sum of Even Numbers

Easy · Algorithms · Topics: language basics

The problem

A primary-school teacher wants a small helper for revision worksheets. Given a number n, it should produce the multiplication table of n from 1 to 10. Given an upper limit, it should produce the sum of all even numbers from 1 to that limit. Both tasks repeat an action a known number of times, which is exactly what a for loop is for. They also expose the three classic loop mistakes: starting at the wrong value, stopping one step early or late, and stepping by the wrong amount.

Example: multiplicationTable(3) → 3 6 9 12 15 18 21 24 27 30; sumOfEvens(10) → 2 + 4 + 6 + 8 + 10 = 30.

Function signature

vector<long long> multiplicationTable(int n);  // n x 1 ... n x 10
long long sumOfEvens(int limit);               // 2 + 4 + ... up to limit

Test cases

Input	Output	Explanation
`multiplicationTable(3)`	`3 6 9 12 15 18 21 24 27 30`	Ten entries, 1 through 10 inclusive
`multiplicationTable(0)`	`0 0 0 0 0 0 0 0 0 0`	Zero times anything is zero
`sumOfEvens(10)`	`30`	2 + 4 + 6 + 8 + 10, where 10 itself is included
`sumOfEvens(7)`	`12`	2 + 4 + 6; 7 is odd so it's not added
`sumOfEvens(1)`	`0`	No even number between 1 and 1
`sumOfEvens(100000)`	`2500050000`	Larger than `INT_MAX`, so the sum needs `long long`

(Confirm: the limit is inclusive and at least 1; the table always has exactly 10 entries.)

How interviewers phrase it

"Print the multiplication table of N." / "Find the sum of the first N natural numbers." / "Sum all even numbers up to N."
Often the first coding question in a fresher or campus interview, used to check that you can write a correct loop without off-by-one errors.
As a follow-up to a loop answer: "Can you do it without a loop?" (testing whether you know the closed-form formula).

Clarifying questions to ask

Is the upper limit inclusive? Should sumOfEvens(10) include 10?
Can the limit be zero or negative?
How large can the limit be? (Decides whether the sum overflows an int.)
Should the function return the values or print them?

Follow-ups to expect

"Why i <= 10 and not i < 10?"
"Can you avoid checking every number for evenness?"
"Can you do it in O(1)?"
"What's the complexity of two nested loops?"
"What's the difference between break and continue?"
"What's a range-based for loop?"

Practise questions like this with a real engineer

On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the expected answer to every follow-up, hints to give if you stall, and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.

Book a free mock interview