DSA interview question

C++ Basics: Data Types, Ranges and Overflow

Easy · Algorithms · Topics: language basics

The problem

An intern built the leaderboard for a coding contest. It reads the scores of every participant and prints the total, the average and the best score. It worked perfectly in testing with five players. On contest day, with 100,000 players scoring up to 10^9 points each, the total came out negative and the average was a whole number even when it shouldn't be. Nothing crashed; the numbers were just silently wrong. Your task: rewrite the summary so it is correct for the real limits, and be able to explain which data type each value needs and why.

Example: scores [1, 2, 3, 4] → Total 10, Average 2.50, Max 4.

Function signature

long long totalScore(const vector<int>& scores);   // sum of all scores
double averageScore(const vector<int>& scores);    // real-valued mean
int maxScore(const vector<int>& scores);           // highest score

Test cases

Input `scores`	Output	Explanation
`[10, 20, 30]`	Total `60`, Average `20.00`, Max `30`	Simple case
`[1, 2, 3, 4]`	Total `10`, Average `2.50`, Max `4`	Integer division would wrongly give 2
`[1000000000, 1000000000, 1000000000]`	Total `3000000000`, Average `1000000000.00`, Max `1000000000`	Total exceeds `INT_MAX` (2147483647), so an `int` sum overflows
`[7]`	Total `7`, Average `7.00`, Max `7`	Single element
`[0, 0]`	Total `0`, Average `0.00`, Max `0`	All zeros

(Confirm: 1 ≤ N ≤ 10^5 and 0 ≤ score ≤ 10^9, so the total can reach 10^14; average printed with 2 decimals.)

How interviewers phrase it

Rarely a standalone question. It shows up as a trap inside another problem: "Sum this array", "Multiply these two numbers", "Find the average", where the constraints quietly make int overflow.
In fresher interviews: "What is the range of an int? When would you use long long?"
As a debugging question: "This code gives a negative sum for large inputs. What's wrong?"

Clarifying questions to ask

What are the maximum values of N and of each element? (Multiply them to get the largest possible total.)
Can values be negative?
Should the average be exact, rounded, or truncated, and to how many decimals?
Can the array be empty? (Division by zero for the average.)

Follow-ups to expect

"What's the range of int and long long?"
"What happens when a signed int overflows?"
"Why does 7 / 2 give 3?"
"long long x = a * b; still overflows even though x is long long. Why?"
"float or double?"
"How big are the basic types?"

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