Aggregate functions (Count, Sum, Average) in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Count example?

Consider this C# code that counts elements in a list:

var numbers = new List<int> {1, 2, 3, 4, 5};
int count = numbers.Count(n => n > 3);
Console.WriteLine(count);

What will be printed?

C Sharp (C#)

var numbers = new List<int> {1, 2, 3, 4, 5};
int count = numbers.Count(n => n > 3);
Console.WriteLine(count);

A 2

B 3

C 5

D 4

💡 Hint

Count counts how many items satisfy the condition.

Only numbers greater than 3 are 4 and 5, so count is 2.

❓ Predict Output

intermediate

What is the sum of these numbers?

Look at this code that sums numbers:

var values = new List<int> {10, 20, 30};
int total = values.Sum();
Console.WriteLine(total);

What is printed?

C Sharp (C#)

var values = new List<int> {10, 20, 30};
int total = values.Sum();
Console.WriteLine(total);

A 0

B 60

C 100

D 30

💡 Hint

Sum adds all numbers in the list.

10 + 20 + 30 equals 60.

❓ Predict Output

advanced

What is the average value computed here?

Analyze this code that calculates average:

var scores = new List<double> {4.0, 5.0, 6.0};
double avg = scores.Average();
Console.WriteLine(avg);

What will be printed?

C Sharp (C#)

var scores = new List<double> {4.0, 5.0, 6.0};
double avg = scores.Average();
Console.WriteLine(avg);

A 5

B 15

C 4

D 6

💡 Hint

Average is total sum divided by count.

(4 + 5 + 6) / 3 = 15 / 3 = 5.

❓ Predict Output

advanced

What error occurs when calling Average on an empty list?

Consider this code:

var emptyList = new List<int>();
double avg = emptyList.Average();
Console.WriteLine(avg);

What happens when this runs?

C Sharp (C#)

var emptyList = new List<int>();
double avg = emptyList.Average();
Console.WriteLine(avg);

A 0

B null

C InvalidOperationException

D DivideByZeroException

💡 Hint

Average on empty collections throws an error.

Calling Average on an empty list throws InvalidOperationException because there is no element to average.

🧠 Conceptual

expert

How many items are counted here?

Given this code:

var data = new List<int> {1, 2, 3, 4, 5, 6};
int count = data.Count(n => n % 2 == 0 && n > 3);
Console.WriteLine(count);

How many items satisfy the condition?

C Sharp (C#)

var data = new List<int> {1, 2, 3, 4, 5, 6};
int count = data.Count(n => n % 2 == 0 && n > 3);
Console.WriteLine(count);

A 4

B 3

C 1

D 2

💡 Hint

Count numbers that are even and greater than 3.

Numbers 4 and 6 are even and greater than 3, so count is 2.