DEV Community

seonglinchua
seonglinchua

Posted on

Mastering Arrays in C# for Coding Interviews

#csharp #datastructures #interview #arrays

🧱 Arrays in C# — A Practical Guide for Interview Preparation

Arrays are one of the most fundamental data structures used in programming and appear frequently in coding interviews.

✅ What is an Array?

An array is a fixed-size, indexed collection of elements of the same type.

✨ Declaring & Initializing Arrays 

// Declare and allocate memory
int[] numbers = new int[5];

// Declare and assign values
int[] scores = new int[] { 90, 85, 78, 92, 88 };

// Short-hand initialization
string[] names = { "Alice", "Bob", "Charlie" };
Enter fullscreen mode Exit fullscreen mode

🔄 Accessing and Updating Elements 

int first = scores[0];
scores[2] = 80;
int last = scores[scores.Length - 1];
Enter fullscreen mode Exit fullscreen mode

🔁 Looping Through Arrays 

// Using for loop
for (int i = 0; i < scores.Length; i++) {
    Console.WriteLine(scores[i]);
}

// Using foreach loop
foreach (int score in scores) {
    Console.WriteLine(score);
}
Enter fullscreen mode Exit fullscreen mode

🔧 Useful Array Operations 

Array.Sort(scores);         // Sort ascending
Array.Reverse(scores);      // Reverse array
int index = Array.IndexOf(scores, 92); // Find index of 92
Enter fullscreen mode Exit fullscreen mode

🧠 Common Use Cases

Use Case Description
Fixed-size data storage e.g., Top 5 student scores
Indexed logic Two pointers, prefix sum, etc.
Brute force comparisons e.g., nested loops for pair matching

🧪 Interview Example: Two Sum (Brute Force) 

public int[] TwoSum(int[] nums, int target) {
    for (int i = 0; i < nums.Length; i++) {
        for (int j = i + 1; j < nums.Length; j++) {
            if (nums[i] + nums[j] == target)
                return new int[] { i, j };
        }
    }
    return new int[] { -1, -1 };
}
Enter fullscreen mode Exit fullscreen mode

📌 Summary

Feature Syntax Example
Declare int[] arr = new int[5];
Access arr[0], arr[arr.Length - 1]
Update arr[2] = 100;
Loop for or foreach
Sort/Reverse Array.Sort(arr), Array.Reverse()

Stay tuned for the next post where we tackle HashSet and use it to solve unique element problems efficiently.

Top comments (1)

Collapse
 
ghost_engineer_2883a1ca0a profile image
Ghost Engineer •

try this if you get stuck during the interview. its an AI co-pilot that solves the questions for you so you can focus on the more important part of the interview, the communication part. its also a really good study tool: ghostengineer.com