Summer Camp Swim Test Results

This last exercise doesn't add a totally new topic so much as it asks you to combine everything so far — a List<T>, a for loop that walks two lists together by index, an if that sets a status and updates a running count, and .Sum() from LINQ — while getting one more subtlety exactly right: integer division. When both sides of a / are int, C# performs integer division and throws away the remainder before the result is ever stored anywhere else, even in a double variable.

Worked example

Here's the same trap with a class's quiz scores:

List<int> scores = new List<int> { 70, 85, 91, 60 };
int totalScore = scores.Sum();
double averageWrong = totalScore / scores.Count;
double averageRight = (double)totalScore / scores.Count;

Console.WriteLine($"Wrong way: {averageWrong}");
Console.WriteLine($"Right way: {averageRight}");

Wrong way: 76
Right way: 76.5

totalScore / scores.Count is 306 / 4, computed entirely with int math first, giving 76 with the .5 thrown away, and only afterward does that truncated 76 get converted to a double for storage. Casting the numerator to double first, with (double)totalScore, forces the division itself to happen in floating point, keeping the .5.

Your turn

The starter code walks a camp's swim test results, labels each camper 'cleared' or 'not yet' based on a required lap count, and then tries to compute the average number of laps completed across everyone. The line double averageLaps = totalLaps / lapsCompleted.Count; divides two int values first, truncating the result, before it ever becomes a double. Fix it so the division itself happens in floating point.

If something goes wrong

If your average always comes out as a whole number when you know the data isn't evenly divisible, that's the integer-division trap — look for a / between two int-typed values and cast one of them to double before the division happens, not after. If the cleared/not-yet labels look wrong, double check the comparison uses >= against the required lap count, not >, since campers who complete exactly the required number should still count as cleared.