C#: C# Examples
1. FizzBuzz
Iterate from 1 to 100: print Fizz for multiples of 3, Buzz for multiples of 5, FizzBuzz for multiples of both, otherwise print the number itself.
▶ Example
CSHARP
using System;
class Program
{
static void Main()
{
for (int i = 1; i <= 100; i++)
{
if (i % 15 == 0)
Console.WriteLine("FizzBuzz");
else if (i % 3 == 0)
Console.WriteLine("Fizz");
else if (i % 5 == 0)
Console.WriteLine("Buzz");
else
Console.WriteLine(i);
}
}
}
TEXT
1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz
16
...
98
Fizz
Buzz
2. Fibonacci Sequence
Print the first 20 numbers of the Fibonacci sequence, where each number is the sum of the two preceding ones.
▶ Example
CSHARP
using System;
class Program
{
static void Main()
{
int a = 0, b = 1;
for (int i = 0; i < 20; i++)
{
Console.Write(a + " ");
int temp = a;
a = b;
b = temp + b;
}
Console.WriteLine();
}
}
TEXT
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597 2584 4181
3. Multiplication Table
Print a classic multiplication table in triangular arrangement.
▶ Example
CSHARP
using System;
class Program
{
static void Main()
{
for (int i = 1; i <= 9; i++)
{
for (int j = 1; j <= i; j++)
{
Console.Write($"{j}x{i}={i * j}\t");
}
Console.WriteLine();
}
}
}
TEXT
1x1=1
1x2=2 2x2=4
1x3=3 2x3=6 3x3=9
1x4=4 2x4=8 3x4=12 4x4=16
1x5=5 2x5=10 3x5=15 4x5=20 5x5=25
1x6=6 2x6=12 3x6=18 4x6=24 5x6=30 6x6=36
1x7=7 2x7=14 3x7=21 4x7=28 5x7=35 6x7=42 7x7=49
1x8=8 2x8=16 3x8=24 4x8=32 5x8=40 6x8=48 7x8=56 8x8=64
1x9=9 2x9=18 3x9=27 4x9=36 5x9=45 6x9=54 7x9=63 8x9=72 9x9=81
4. Prime Check
Determine whether a user-input positive integer is prime and print the result.
▶ Example
CSHARP
using System;
class Program
{
static bool IsPrime(int n)
{
if (n < 2) return false;
for (int i = 2; i * i <= n; i++)
{
if (n % i == 0) return false;
}
return true;
}
static void Main()
{
int number = 29;
if (IsPrime(number))
Console.WriteLine($"{number} is prime");
else
Console.WriteLine($"{number} is not prime");
number = 35;
if (IsPrime(number))
Console.WriteLine($"{number} is prime");
else
Console.WriteLine($"{number} is not prime");
}
}
TEXT
29 is prime
35 is not prime
5. Palindrome Detection
Determine whether a string is a palindrome (reads the same forward and backward).
▶ Example
CSHARP
using System;
class Program
{
static bool IsPalindrome(string s)
{
int left = 0, right = s.Length - 1;
while (left < right)
{
if (s[left] != s[right]) return false;
left++;
right--;
}
return true;
}
static void Main()
{
string[] tests = { "racecar", "hello", "level", "world" };
foreach (string t in tests)
{
Console.WriteLine($"{t} -> {(IsPalindrome(t) ? "is palindrome" : "is not palindrome")}");
}
}
}
TEXT
racecar -> is palindrome
hello -> is not palindrome
level -> is palindrome
world -> is not palindrome
6. Reverse String
Reverse an input string and print the result.
▶ Example
CSHARP
using System;
class Program
{
static string ReverseString(string s)
{
char[] arr = s.ToCharArray();
Array.Reverse(arr);
return new string(arr);
}
static void Main()
{
string original = "Hello CSharp";
string reversed = ReverseString(original);
Console.WriteLine($"Original: {original}");
Console.WriteLine($"Reversed: {reversed}");
}
}
TEXT
Original: Hello CSharp
Reversed: prahSC olleH
7. Count Vowels
Count the occurrences of vowel letters (a, e, i, o, u, case-insensitive) in a string.
▶ Example
CSHARP
using System;
class Program
{
static int CountVowels(string s)
{
int count = 0;
string vowels = "aeiouAEIOU";
foreach (char c in s)
{
if (vowels.IndexOf(c) >= 0)
count++;
}
return count;
}
static void Main()
{
string text = "Hello World Programming";
int result = CountVowels(text);
Console.WriteLine($"String: {text}");
Console.WriteLine($"Vowel count: {result}");
}
}
TEXT
String: Hello World Programming
Vowel count: 6
8. File I/O
Demonstrate basic text file write and read operations.
▶ Example
CSHARP
using System;
using System.IO;
class Program
{
static void Main()
{
string path = "test.txt";
string[] lines = { "First line", "Second line", "Third line" };
File.WriteAllLines(path, lines);
Console.WriteLine("Write complete");
string[] readLines = File.ReadAllLines(path);
Console.WriteLine("Read content:");
foreach (string line in readLines)
{
Console.WriteLine(line);
}
File.Delete(path);
}
}
TEXT
Write complete
Read content:
First line
Second line
Third line
9. Number Guessing Game
The program generates a random integer between 1 and 100. The player makes guesses and the program hints whether the guess is too high or too low until the correct number is found.
▶ Example
CSHARP
using System;
class Program
{
static void Main()
{
Random rnd = new Random(42);
int target = rnd.Next(1, 101);
int[] guesses = { 50, 75, 62, 68, 71, 73, 72 };
int attempts = 0;
Console.WriteLine($"Target number: {target} (shown for demo only)");
Console.WriteLine("---");
foreach (int guess in guesses)
{
attempts++;
if (guess < target)
Console.WriteLine($"Attempt {attempts}: {guess} - Too low");
else if (guess > target)
Console.WriteLine($"Attempt {attempts}: {guess} - Too high");
else
{
Console.WriteLine($"Attempt {attempts}: {guess} - Correct!");
break;
}
}
}
}
TEXT
Target number: 72 (shown for demo only)
---
Attempt 1: 50 - Too low
Attempt 2: 75 - Too high
Attempt 3: 62 - Too low
Attempt 4: 68 - Too low
Attempt 5: 71 - Too low
Attempt 6: 73 - Too high
Attempt 7: 72 - Correct!
10. Student Grade Calculator
Given a set of student grades, calculate the average, highest, and lowest scores.
▶ Example
CSHARP
using System;
using System.Linq;
class Program
{
static void Main()
{
double[] scores = { 85.5, 92.0, 78.5, 96.0, 88.0, 73.5, 91.0 };
double average = scores.Average();
double max = scores.Max();
double min = scores.Min();
Console.WriteLine("Student grades: " + string.Join(", ", scores));
Console.WriteLine($"Average: {average:F1}");
Console.WriteLine($"Highest: {max:F1}");
Console.WriteLine($"Lowest: {min:F1}");
}
}
TEXT
Student grades: 85.5, 92, 78.5, 96, 88, 73.5, 91
Average: 86.4
Highest: 96.0
Lowest: 73.5
❓ FAQ
Q How do I run these C# examples?
A Copy the code into a .cs file and run with dotnet run, or use an online C# compiler like dotnetfiddle.net.
Q Can I modify the examples and see results?
A Yes! Save the file and run dotnet run again. C# compiles to bytecode, so changes take effect immediately.
Q Where are the larger examples?
A See lesson 36 — the Final Project. This index only collects short, single-concept snippets.
📖 Summary
- Each example is self-contained — copy and run in any C# environment
- Examples focus on one concept at a time
- Modify freely to explore behavior
- For larger projects, see the dedicated lessons
📝 Exercises
- Pick any example, modify it, and document the new behavior in a comment.
- Combine two examples (e.g., variables + events) into a single program.
- Create your own example page teaching a concept you find confusing.
