C#

Question 1

How do you read all lines from a text file in C#?

Answer 1

string[] lines = File.ReadAllLines(“filename.txt”);

Question 2

How do you write all lines to a text file in C#?

Answer 2

File.WriteAllLines(“filename.txt”, lines);

Question 3

How do you use a foreach loop in C# to print every item in an array?

Answer 3

foreach (var item in array) { Console.WriteLine(item); }

Question 4

How do you write a while loop that continues until x equals 10?

Answer 4

while (x != 10) { // code here }

Question 5

How do you ask a user for input from the console in C#?

Answer 5

Console.WriteLine(“Enter your name:”); string name = Console.ReadLine();

Question 6

How do you convert a string to an integer in C#?

Answer 6

int number = int.Parse(Console.ReadLine());

Question 7

How do you split a string by spaces in C#?

Answer 7

string[] words = sentence.Split(‘ ‘);

Question 8

How do you iterate over an array with a for loop in C#?

Answer 8

for (int i = 0; i < array.Length; i++) { Console.WriteLine(array[i]); }

Question 9

How do you implement bubble sort in C#?

Answer 9

for (int i = 0; i < arr.Length - 1; i++) { for (int j = 0; j < arr.Length - i - 1; j++) { if (arr[j] > arr[j + 1]) { var temp = arr[j]; arr[j] = arr[j + 1]; arr[j + 1] = temp; }}}

Question 10

How do you implement merge sort in C# (overview)?

Answer 10

Split the array into halves, recursively sort each half, and merge them. See next card for code.

Question 11

What is a simple example of merge sort in C#?

Answer 11

void MergeSort(int[] array) { if (array.Length <= 1) return; int mid = array.Length / 2; int[] left = array[..mid]; int[] right = array[mid..]; MergeSort(left); MergeSort(right); Merge(array, left, right); }

Question 12

How do you define a class in C#?

Answer 12

public class Person { public string Name; public int Age; }

Question 13

How do you create an object from a class in C#?

Answer 13

Person p = new Person(); p.Name = “Alice”; p.Age = 30;

Question 14

What is a constructor in C#?

Answer 14

A constructor is a method that runs when an object is created: public Person(string name) { Name = name; }

Question 15

How do you use inheritance in C#?

Answer 15

class Student : Person { public string School; }

Question 16

What is polymorphism in C#?

Answer 16

Polymorphism allows methods to behave differently depending on the object. Use virtual and override keywords.

Question 17

How do you declare a method in C#?

Answer 17

public int Add(int a, int b) { return a + b; }

Question 18

What is the difference between == and .Equals() in C#?

Answer 18

== compares value or reference depending on the type; .Equals() is a method you can override for custom comparison.

Question 19

How do you check if a string contains another string in C#?

Answer 19

if (text.Contains(“keyword”)) { /* code */ }

Question 20

How do you convert a number to a string in C#?

Answer 20

string s = number.ToString();

Question 21

How do you parse a string into a double safely in C#?

Answer 21

double.TryParse(input, out double result);

Question 22

How do you define and use an array in C#?

Answer 22

int[] numbers = {1, 2, 3}; Console.WriteLine(numbers[0]);

Question 23

How do you define a list and add to it in C#?

Answer 23

List<int> nums = new List<int>(); nums.Add(5);</int></int>

Question 24

How do you use a switch statement in C#?

Answer 24

switch (value) { case 1: Console.WriteLine(“One”); break; default: Console.WriteLine(“Other”); break; }

Question 25

How do you handle exceptions in C#?

Answer 25

try { /* code */ } catch (Exception ex) { Console.WriteLine(ex.Message); }

Question 26

How do you define and access a tuple in C#?

Answer 26

var person = (25, "Alice"); Console.WriteLine(person.Item1);

Question 27

How do you give names to tuple elements in C#?

Answer 27

var person = (age: 25, name: "Alice"); Console.WriteLine(person.name);

Question 28

How do you declare and use a Dictionary in C#?

Answer 28

var dict = new Dictionary(); dict["age"] = 30;

Question 29

How do you iterate over a Dictionary in C#?

Answer 29

foreach (var pair in dict) { Console.WriteLine(pair.Key + ": " + pair.Value); }

Question 30

How do you cast a double to an int in C#?

Answer 30

int x = (int)3.7; // result: 3

Question 31

How do you safely convert a string to an int in C#?

Answer 31

if (int.TryParse(input, out int result)) { /* use result */ }

Question 32

How do you make a string uppercase in C#?

Answer 32

string upper = myString.ToUpper();

Question 33

How do you replace part of a string in C#?

Answer 33

string newStr = str.Replace("old", "new");

Question 34

How do you get a substring from a string in C#?

Answer 34

string part = str.Substring(0, 5);

Question 35

How do you define an enum in C#?

Answer 35

enum Days { Monday, Tuesday, Wednesday }

Question 36

How do you use an enum in C#?

Answer 36

Days today = Days.Monday; Console.WriteLine((int)today);

Question 37

How do you create and use a Queue in C#?

Answer 37

Queue queue = new Queue(); queue.Enqueue(1); int first = queue.Dequeue();

Question 38

How do you create and use a Stack in C#?

Answer 38

Stack stack = new Stack(); stack.Push(1); int last = stack.Pop();

Question 39

What is recursion in C#?

Answer 39

A method that calls itself. Useful for problems like factorial, Fibonacci, tree traversal.

Question 40

Write a simple recursive factorial method in C#

Answer 40

int Factorial(int n) { return n <= 1 ? 1 : n * Factorial(n - 1); }

Question 41

What are access modifiers in C#?

Answer 41

They control visibility: public (anywhere), private (class only), protected (class + subclass), internal (same assembly)

Question 42

When should you use 'private' in C#?

Answer 42

Use private to hide class internals from other parts of the program.

Question 43

What is the purpose of 'public' in C#?

Answer 43

Use public for methods or properties you want accessible from other classes.

Question 44

How do you generate a random number in C#?

Answer 44

Random rand = new Random(); int n = rand.Next(1, 101); // 1 to 100

Question 45

How do you round a number to the nearest integer in C#?

Answer 45

double rounded = Math.Round(3.6);

Question 46

How do you get the square root of a number in C#?

Answer 46

double root = Math.Sqrt(25); // 5

Question 47

How do you get the current date and time in C#?

Answer 47

DateTime now = DateTime.Now;

Question 48

How do you format a DateTime as a string in C#?

Answer 48

string formatted = now.ToString("dd/MM/yyyy HH:mm");

Question 49

How do you add days to the current date in C#?

Answer 49

DateTime tomorrow = DateTime.Now.AddDays(1);