How to Find Index of First Vowel in a String

how to find index of first vowel in a string?

First of all, your break should break out of both loops. To do so, put a flag before your first loop like

outerloop:
for (int i = 0; i < word.length(); i++) {

Then instead of break; put break outerloop;

Second,

word = word.substring(i + 1) + word.substring(i) + "ay";

doesn't work, because when you find the vowel, you want to keep it in front, so i + 1 should be just i. Then, the rest of the substring before "ay" should be the consonants at the beginning, so 0, i instead of just i. In all, this gives

outerloop:
    for (int i = 0; i < word.length(); i++) {
        for (int j = 0; j < 5; j++) {
            if (word.charAt(i) == vowel[j]) {
                word = word.substring(i) + word.substring(0, i) + "ay";
                break outerloop;
            }
        }
    }

Finding where the first vowel in a word occurs

Here's one way you could do it:

final static String vowels = "aeiouy";
public static int indexOfFirstVowel(String word){
    String loweredWord = word.toLowerCase();

    for (int index = 0; index < loweredWord.length(); index++)
    {
        if (vowels.contains(String.valueOf(loweredWord.charAt(index))))
        {
            return index;
        }
    }

    // handle cases where a vowel is not found
    return -1;
}

This simply walks through the word by character, and checks each character to see if it exists within your vowels String.

Extract the index of the first vowel in a string

Here is a solution using a simple For loop which you might be familiar with and enumerate:

def position_of_first_vowel(word):
  for index, char in enumerate(word):
    if char in 'aeiou':
      return index
  return -1

for case in ["python","stock", "overflow", "styling", "zxc"]:
  print("%s: %d" % (case, position_of_first_vowel(case)))

Output:

python: 4
stock: 2
overflow: 0
styling: 4
zxc: -1

N.B. The extra test case of zxc is there to show the returning of -1 if a vowel does not occur in the word

Find first vowel from string and add it to a var

You do not need to add the date part by part to avoid -, it is better to split it by - and join the parts together to get desired result. And you can use a loop to find first vowel:

private String getRFC(){
    String vowels = "AEIOUaeiou";

    String apellidoPat = "CRUZ";
    String apellidoMat = "HERNANDEZ";
    String fechaNac = "1997-12-25";

    // first letter of apellidoPat
    String rfc = String.valueOf(apellidoPat.charAt(0));

    //  first vowel of apellidoPat
    for (int i = 0; i < apellidoPat.length(); ++i){
        if (vowels.indexOf(apellidoPat.charAt(i)) != -1){
            rfc += String.valueOf(apellidoPat.charAt(i));
            break;
        }
    }

    // first letter of apellidoMat + date (YYMMDD)
    rfc += apellidoMat.charAt(0) + String.join("", fechaNac.split("-"));

    return rfc;
}

Finding first vowel of a word in Python

Your code always return len(word)-1 if the character in position 1 is not a vowel. Also elephant didn't work and spa works only because of the bug I mentioned, it returns 2 which is len(word)-1 and not the index of the vowel found. Try debug your code line by line and you'll figure it out very quickly.

This could be a working code that return -1 if there's no vowel, else return the index of the first vowel found.

def find_first_vowel(word):
    i = 0   
    while i < len(word):
        if word[i] in vowels:
            return i
        i += 1
    return -1

EDIT

If you want to return the last character if there's no vowels just change return -1 with return len(word) - 1. Here:

def find_first_vowel(word):
    i = 0   
    while i < len(word):
        if word[i] in vowels:
            return i
        i += 1
    return len(word) - 1

Finding the first index of a vowel in a given string, otherwise return -1 if there aren't any

You're getting the int repesentation of the char, you actually want to return i as this shows the position where you found the char.

I need to find the position of the first vowel in a string in php

Use the strcspn function. It will return the length of the string at the beginning not matching any of the characters you specified.

$pos = strcspn(strtolower($str), "aeiou"); // and sometimes y

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