Example: Remove Vowels from String in C

// Remove Vowels from String
#include <stdio.h>
#include <string.h> // For strlen
#include <ctype.h>  // For tolower

// Function to check if a character is a vowel
int isVowel(char c) {
    c = tolower(c); // Convert to lowercase for easier comparison
    return (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u');
}

// Function to remove vowels from a string (in-place)
void removeVowels(char* str) {
    // Step 1: Initialize two pointers: 'readIndex' to traverse the original string
    // and 'writeIndex' to place non-vowel characters in the modified string.
    int readIndex = 0;
    int writeIndex = 0;

    // Step 2: Loop through the string until the null terminator is encountered.
    while (str[readIndex] != '\0') {
        // Step 3: Check if the character at 'readIndex' is a vowel.
        if (!isVowel(str[readIndex])) {
            // Step 4: If it's NOT a vowel, copy it to the 'writeIndex' position.
            str[writeIndex] = str[readIndex];
            // Step 5: Increment 'writeIndex' to prepare for the next non-vowel.
            writeIndex++;
        }
        // Step 6: Always increment 'readIndex' to move to the next character in the original string.
        readIndex++;
    }
    // Step 7: After the loop, null-terminate the modified string at 'writeIndex'.
    str[writeIndex] = '\0';
}

int main() {
    char str1[] = "Hello World";
    char str2[] = "Programming Is Fun";
    char str3[] = "AEIOUaeiou";
    char str4[] = "Rhythm";

    printf("Original string: \"%s\"\n", str1);
    removeVowels(str1);
    printf("After removing vowels: \"%s\"\n\n", str1);

    printf("Original string: \"%s\"\n", str2);
    removeVowels(str2);
    printf("After removing vowels: \"%s\"\n\n", str2);

    printf("Original string: \"%s\"\n", str3);
    removeVowels(str3);
    printf("After removing vowels: \"%s\"\n\n", str3);

    printf("Original string: \"%s\"\n", str4);
    removeVowels(str4);
    printf("After removing vowels: \"%s\"\n\n", str4);

    return 0;
}