C# Program to Check Vowel or Consonant

In C#, you can check if a character is a vowel or consonant by using char.ToLower() to normalize the input and then comparing it with vowels using if statements, for example: if ("aeiou".Contains(char.ToLower(ch))) Console.WriteLine("Vowel"); else Console.WriteLine("Consonant");.

Examples

Inputa

OutputVowel

InputB

OutputConsonant

Inputz

OutputConsonant

How to Think About It

To check if a letter is a vowel or consonant, first convert the letter to lowercase to handle both uppercase and lowercase inputs. Then check if this lowercase letter is one of the vowels 'a', 'e', 'i', 'o', or 'u'. If yes, it is a vowel; otherwise, it is a consonant.

Algorithm

1

Get a single character input from the user.

2

Convert the character to lowercase to simplify comparison.

3

Check if the character is in the set of vowels (a, e, i, o, u).

4

If it is a vowel, print 'Vowel'.

5

Otherwise, print 'Consonant'.

Code

csharp

using System;
class Program {
    static void Main() {
        Console.Write("Enter a letter: ");
        char ch = Console.ReadKey().KeyChar;
        Console.WriteLine();
        char lowerCh = char.ToLower(ch);
        if ("aeiou".Contains(lowerCh))
            Console.WriteLine("Vowel");
        else
            Console.WriteLine("Consonant");
    }
}

Output

Enter a letter: a
Vowel

Dry Run

Let's trace input 'B' through the code

1

Input character

User inputs 'B'

2

Convert to lowercase

'B' becomes 'b'

3

Check if vowel

'b' is checked against 'aeiou' and is not found

4

Print result

Print 'Consonant'

Step	Character	Lowercase	Is Vowel?	Output
1	B	b	No	Consonant

Why This Works

Step 1: Normalize input

Using char.ToLower() ensures the program treats uppercase and lowercase letters the same.

Step 2: Check vowels

The program checks if the lowercase character is in the string "aeiou", which contains all vowels.

Step 3: Output result

If the character is found in vowels, it prints Vowel, otherwise it prints Consonant.

Alternative Approaches

Using switch statement

csharp

using System;
class Program {
    static void Main() {
        Console.Write("Enter a letter: ");
        char ch = char.ToLower(Console.ReadKey().KeyChar);
        Console.WriteLine();
        switch (ch) {
            case 'a': case 'e': case 'i': case 'o': case 'u':
                Console.WriteLine("Vowel");
                break;
            default:
                Console.WriteLine("Consonant");
                break;
        }
    }
}

Switch is clear and easy to read but slightly longer than string.Contains.

Using HashSet for vowels

csharp

using System;
using System.Collections.Generic;
class Program {
    static void Main() {
        var vowels = new HashSet<char>{'a','e','i','o','u'};
        Console.Write("Enter a letter: ");
        char ch = char.ToLower(Console.ReadKey().KeyChar);
        Console.WriteLine();
        if (vowels.Contains(ch))
            Console.WriteLine("Vowel");
        else
            Console.WriteLine("Consonant");
    }
}

HashSet lookup is very fast and good for larger sets but overkill for just vowels.

Complexity: O(1) time, O(1) space

Time Complexity

Checking if a character is in a small fixed set of vowels is constant time, O(1), because the set size does not grow.

Space Complexity

The program uses a fixed amount of space for the vowel set and variables, so space complexity is O(1).

Which Approach is Fastest?

Using string.Contains or a switch statement both run in constant time; HashSet is also O(1) but uses more memory.

Approach	Time	Space	Best For
string.Contains	O(1)	O(1)	Simple and readable for small sets
switch statement	O(1)	O(1)	Clear control flow, easy to extend
HashSet lookup	O(1)	O(n)	Fast lookup for larger sets, more memory