Example: Count Vowels Helper Function in C

// Count Vowels Helper Function
#include <stdio.h>
#include <string.h> // For strlen()
#include <ctype.h>  // For tolower()

// Function to check if a character is a vowel (case-insensitive)
int isVowel(char c) {
    char lower_c = tolower(c); // Convert to lowercase
    if (lower_c == 'a' || lower_c == 'e' || lower_c == 'i' || lower_c == 'o' || lower_c == 'u') {
        return 1; // It's a vowel
    }
    return 0; // It's not a vowel
}

int main() {
    // Step 1: Declare a character array (string) and a counter for vowels.
    char str[100];
    int vowelCount = 0;
    int i; // Loop counter

    // Step 2: Prompt the user to enter a string.
    printf("Enter a string: ");
    
    // Step 3: Read the string from the user.
    fgets(str, sizeof(str), stdin);

    // Step 4: Remove the trailing newline character if it exists.
    str[strcspn(str, "\n")] = 0;

    // Step 5: Iterate through the string character by character.
    for (i = 0; str[i] != '\0'; i++) {
        // Step 6: Call the helper function to check if the current character is a vowel.
        if (isVowel(str[i])) {
            vowelCount++;
        }
    }

    // Step 7: Print the total count of vowels.
    printf("Number of vowels in the string: %d\n", vowelCount);

    return 0;
}