Array iteration with for and foreach in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of for loop iterating over an array

What is the output of the following C# code?

C Sharp (C#)

int[] numbers = {1, 2, 3};
for (int i = 0; i < numbers.Length; i++)
{
    Console.Write(numbers[i] + " ");
}

A 0 1 2

B 1 2 3

C 123

D 1 2 3 4

💡 Hint

Remember that Console.Write prints without a newline and the loop prints each element followed by a space.

The for loop iterates over each element in the array and prints it followed by a space, resulting in '1 2 3 '.

❓ Predict Output

intermediate

Output of foreach loop with array

What will this C# code print?

C Sharp (C#)

string[] fruits = {"apple", "banana", "cherry"};
foreach (string fruit in fruits)
{
    Console.Write(fruit[0]);
}

A abc

B applebanana cherry

C a b c

D apple

💡 Hint

Each fruit's first character is printed without spaces.

The foreach loop prints the first character of each fruit, resulting in 'abc'.

❓ Predict Output

advanced

Value of sum after mixed iteration

What is the value of sum after running this code?

C Sharp (C#)

int[] values = {2, 4, 6};
int sum = 0;
for (int i = 0; i < values.Length; i++)
{
    sum += values[i];
}
foreach (int v in values)
{
    sum += v;
}

A 6

B 12

C 18

D 24

💡 Hint

The for loop adds all elements once, then the foreach adds them again.

The sum is 2+4+6 = 12 from the for loop, then 12 more from the foreach, total 24.

❓ Predict Output

advanced

Output of modifying array inside foreach

What happens when this code runs?

C Sharp (C#)

int[] nums = {1, 2, 3};
foreach (int n in nums)
{
    n = n * 2;
    Console.Write(n + " ");
}
Console.WriteLine();
foreach (int n in nums)
{
    Console.Write(n + " ");
}

A

2 4 6 
1 2 3 

B

2 4 6 
2 4 6 

C

1 2 3 
1 2 3 

D Compilation error

💡 Hint

Foreach variable is read-only copy, modifying it does not change the array.

The first loop prints doubled values but does not change the array. The second loop prints original values.

🧠 Conceptual

expert

Why does modifying array elements inside foreach cause error?

Consider this code snippet: int[] arr = {1, 2, 3}; foreach (int x in arr) { x = x + 1; } Why does this code not modify the array elements?

A Because the compiler automatically resets the array after the loop finishes.

B Because arrays in C# are immutable and cannot be changed after creation.

C Because the foreach variable 'x' is a copy of each element, not a reference, so changes don't affect the array.

D Because the foreach loop does not allow any statements inside its block.

💡 Hint

Think about how foreach handles the loop variable.

In C#, foreach assigns each element's value to the loop variable as a copy. Modifying the variable does not change the original array element.