How to count number of vowels and consonants in a string in C Language?

In C programming, counting vowels and consonants in a string is a common string manipulation task. We iterate through each character and check if it's a vowel (a, e, i, o, u) or consonant using conditional statements.

Syntax

// Check if character is vowel
if(ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u' ||
   ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U')
    vowels++;
else if(isalpha(ch))
    consonants++;

Method 1: Using Character Comparison

This approach checks each character against all vowel possibilities and counts alphabetic non-vowels as consonants −

#include <stdio.h>
#include <ctype.h>

int main() {
    char str[100];
    int i, vowels, consonants;
    i = vowels = consonants = 0;
    
    printf("Enter a string: ");
    fgets(str, sizeof(str), stdin);
    
    while (str[i] != '\0') {
        if (isalpha(str[i])) {
            if (str[i] == 'A' || str[i] == 'E' || str[i] == 'I' || 
                str[i] == 'O' || str[i] == 'U' || str[i] == 'a' || 
                str[i] == 'e' || str[i] == 'i' || str[i] == 'o' || 
                str[i] == 'u') {
                vowels++;
            } else {
                consonants++;
            }
        }
        i++;
    }
    
    printf("Vowels: %d
", vowels);
    printf("Consonants: %d
", consonants);
    return 0;
}

Enter a string: TutorialsPoint
Vowels: 6
Consonants: 8

Method 2: Using Switch Statement

A cleaner approach using switch-case for vowel detection −

#include <stdio.h>
#include <ctype.h>

int main() {
    char str[] = "Programming";
    int i, vowels = 0, consonants = 0;
    
    printf("String: %s
", str);
    
    for (i = 0; str[i] != '\0'; i++) {
        if (isalpha(str[i])) {
            switch (tolower(str[i])) {
                case 'a':
                case 'e':
                case 'i':
                case 'o':
                case 'u':
                    vowels++;
                    break;
                default:
                    consonants++;
                    break;
            }
        }
    }
    
    printf("Vowels: %d
", vowels);
    printf("Consonants: %d
", consonants);
    return 0;
}

String: Programming
Vowels: 3
Consonants: 8

Key Points

• Use isalpha() to check if a character is alphabetic before counting
• The tolower() function simplifies vowel checking by converting to lowercase
• Non-alphabetic characters (spaces, digits, symbols) are ignored in the count
• Always use fgets() instead of gets() for safe string input

Conclusion

Counting vowels and consonants in C involves iterating through the string and using conditional logic to categorize alphabetic characters. The switch-case method provides cleaner code for vowel detection.