Null-coalescing operator in C Sharp (C#) - Time & Space Complexity

Time Complexity: Null-coalescing operator

O(n)

Understanding Time Complexity

Let's see how the null-coalescing operator affects the time it takes for a program to run.

We want to know how the number of steps changes as input size grows.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

string? GetName(string? input)
{
    return input ?? "Default";
}

string?[] names = new string?[1000];
for (int i = 0; i < names.Length; i++)
{
    string name = GetName(names[i]);
}
    

This code uses the null-coalescing operator to return a default string if the input is null, repeated over an array.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Looping through the array of strings.
• How many times: Once for each element in the array (n times).

How Execution Grows With Input

Each element is checked once with the null-coalescing operator.

Input Size (n)	Approx. Operations
10	10 checks
100	100 checks
1000	1000 checks

Pattern observation: The number of operations grows directly with the input size.

Final Time Complexity

Time Complexity: O(n)

This means the time to run grows in a straight line as the input size grows.

Common Mistake

[X] Wrong: "The null-coalescing operator makes the code run instantly regardless of input size."

[OK] Correct: Even though the operator is simple, it still runs once per item, so time grows with input size.

Interview Connect

Understanding how simple operators affect time helps you explain your code clearly and shows you think about efficiency.

Self-Check

"What if we replaced the loop with a recursive call over the array? How would the time complexity change?"