Program to count vowels in a string (Iterative and Recursive)

Given a string, count the total number of vowels (a, e, i, o, u) in it. There are two methods to count total number of vowels in a string. 

1. Iterative 
2. Recursive

Examples:

Input : abc de
Output : 2

Input : geeksforgeeks portal
Output : 7

1. Iterative Method:

Below is the implementation: 

C++

// C++ program to count vowels in a string
#include<iostream>
using namespace std;

// Function to check the Vowel
bool isVowel(char ch)
{
    ch = toupper(ch);
    return (ch=='A' || ch=='E' || ch=='I' ||
                       ch=='O' || ch=='U');
}

// Returns count of vowels in str
int countVowels(string str)
{
    int count = 0;
    for (int i=0; i<str.length(); i++)
        if (isVowel(str[i])) // Check for vowel
            ++count;
    return count;
}

// Main Calling Function
int main()
{
    //string object
    string str = "abc de";

    // Total numbers of Vowel
    cout << countVowels(str) << endl;
    return 0;
}

Java

// Java program to count vowels in a string
public class GFG {

    // Function to check the Vowel
    static boolean isVowel(char ch)
    {
        ch = Character.toUpperCase(ch);
        return (ch=='A' || ch=='E' || ch=='I' ||
                           ch=='O' || ch=='U');
    }

    // Returns count of vowels in str
    static int countVowels(String str)
    {
        int count = 0;
        for (int i = 0; i < str.length(); i++)
            if (isVowel(str.charAt(i))) // Check for vowel
                ++count;
        return count;
    }

    // Driver code
    public static void main(String args[])
    {
        //string object
        String str = "abc de";

        // Total numbers of Vowel
        System.out.println(countVowels(str));
    }
}
// This code is contributed by Sumit Ghosh

Python3

# Python3 program to count vowels
# in a string

# Function to check the Vowel
def isVowel(ch):
    return ch.upper() in ['A', 'E', 'I', 'O', 'U']

# Returns count of vowels in str
def countVowels(str):
    count = 0
    for i in range(len(str)):

        # Check for vowel
        if isVowel(str[i]):
            count += 1
    return count

# Driver Code

# string object
str = 'abc de'

# Total number of Vowels
print(countVowels(str))

# This code is contributed
# by SamyuktaSHegde

C#

// C# program to count vowels in a string
using System;

class GFG
{

    // Function to check the Vowel
    public static bool isVowel(char ch)
    {
        ch = char.ToUpper(ch);
        return (ch == 'A' || ch == 'E' ||
                ch == 'I' || ch == 'O' ||
                              ch == 'U');
    }

    // Returns count of vowels in str
    public static int countVowels(string str)
    {
        int count = 0;
        for (int i = 0; i < str.Length; i++)
        {

            // Check for vowel
            if (isVowel(str[i]))
            {
                ++count;
            }
        }
        return count;
    }

    // Driver code
    public static void Main(string[] args)
    {

        //string object
        string str = "abc de";

        // Total numbers of Vowel
        Console.WriteLine(countVowels(str));
    }
}

// This code is contributed by Shrikant13

PHP

<?php
// PHP program to count vowels in a string

// Function to check the Vowel
function isVowel($ch)
{
    $ch = strtoupper($ch);
    return ($ch =='A' || $ch =='E' ||
            $ch =='I' || $ch =='O' ||
            $ch =='U');
}

// Returns count of vowels in str
function countVowels($str)
{
    $count = 0;
    for ($i = 0; $i < strlen($str); $i++)
        if (isVowel($str[$i])) // Check for vowel
            ++$count;
    return $count;
}

// Driver Code

//string object
$str = "abc de";

// Total numbers of Vowel
echo countVowels($str) . "\n";

// This code is contributed
// by Akanksha Rai
?>

Javascript

<script>
      // JavaScript program to count vowels in a string

      // Function to check the Vowel
      function isVowel(ch) {
        ch = ch.toUpperCase();
        return ch == "A" || ch == "E" || ch == "I" || ch == "O" || ch == "U";
      }

      // Returns count of vowels in str
      function countVowels(str)
      {
        var count = 0;
        for (var i = 0; i < str.length; i++)
          if (isVowel(str[i]))

            // Check for vowel
            ++count;
        return count;
      }

      // Main Calling Function

      // string object
      var str = "abc de";

      // Total numbers of Vowel
      document.write(countVowels(str));
      document.write("<br>");

      // This code is contributed by rdtank.
    </script>

Output

2

Time Complexity: O(n), where n is the length of the string
Auxiliary Space: O(1) 

2. Recursive Method:

Below is the implementation: 

C++

// Recursive C++ program to count the total
// number of vowels using recursion
#include<iostream>
using namespace std;

// Function to check the Vowel
bool isVowel(char ch)
{
    ch = toupper(ch);
    return (ch=='A' || ch=='E' || ch=='I' ||
                        ch=='O' || ch=='U');
}

// to count total number of vowel from 0 to n
int countVovels(string str, int n)
{
    if (n == 1)
        return isVowel(str[n-1]);

    return countVovels(str, n-1) + isVowel(str[n-1]);
}

// Main Calling Function
int main()
{
    // string object
    string str = "abc de";

    // Total numbers of Vowel
    cout << countVovels(str, str.length()) << endl;
    return 0;
}

Java

// Recursive Java program to count the total
// number of vowels using recursion
public class GFG {

    // Function to check the Vowel
    static int isVowel(char ch)
    {
        ch = Character.toUpperCase(ch);
       if(ch=='A' || ch=='E' || ch=='I' ||
            ch=='O' || ch=='U')
           return 1;
       else return 0;
    }

    // to count total number of vowel from 0 to n
    static int countVowels(String str, int n)
    {
        if (n == 1)
            return isVowel(str.charAt(n - 1));

        return countVowels(str, n-1) + isVowel(str.charAt(n - 1));
    }

    // Main Calling Function
    public static void main(String args[])
    {
        //string object
        String str = "abc de";

        // Total numbers of Vowel
        System.out.println(countVowels(str,str.length()));
    }
}
// This code is contributed by Sumit Ghosh

Python 3

# Recursive Python 3 program to count the
# total number of vowels using recursion

# Function to check the Vowel
def isVowel(ch):
    return ch.upper() in ['A', 'E', 'I', 'O', 'U']

# to count total number of
# vowel from 0 to n
def countVovels(str, n):
    if (n == 1):
        return isVowel(str[n - 1]);

    return (countVovels(str, n - 1) +
                isVowel(str[n - 1]));

# Driver Code

# string object
str = "abc de";

# Total numbers of Vowel
print(countVovels(str, len(str)))

# This code is contributed
# by Akanksha Rai

C#

using System;

// Recursive C# program to count the total
// number of vowels using recursion
public class GFG
{

    // Function to check the Vowel
    public static int isVowel(char ch)
    {
        ch = char.ToUpper(ch);
       if (ch == 'A' || ch == 'E' || ch == 'I' || ch == 'O' || ch == 'U')
       {
           return 1;
       }
       else
       {
           return 0;
       }
    }

    // to count total number of vowel from 0 to n
    public static int countVowels(string str, int n)
    {
        if (n == 1)
        {
            return isVowel(str[n - 1]);
        }

        return countVowels(str, n - 1) + isVowel(str[n - 1]);
    }

    // Main Calling Function
    public static void Main(string[] args)
    {
        //string object
        string str = "abc de";

        // Total numbers of Vowel
        Console.WriteLine(countVowels(str,str.Length));
    }
}

// This code is contributed by Shrikant13

PHP

<?php
// Recursive PHP program to count the total
// number of vowels using recursion

// Function to check the Vowel
function isVowel($ch)
{
    $ch = strtoupper($ch);
    return ($ch == 'A' || $ch == 'E' ||
            $ch == 'I' || $ch == 'O' ||
            $ch == 'U');
}

// to count total number of
// vowel from 0 to n
function countVovels($str, $n)
{
    if ($n == 1)
        return isVowel($str[$n - 1]);

    return countVovels($str, $n - 1) +
               isVowel($str[$n - 1]);
}

// Driver Code

// string object
$str = "abc de";

// Total numbers of Vowel
echo countVovels($str, strlen($str)) . "\n";

// This code is contributed
// by Akanksha Rai
?>

Javascript

<script>

// Recursive JavaScript program to count the total
// number of vowels using recursion

// Function to check the Vowel
function isVowel(ch)
{
    ch = ch.toUpperCase();
    return (ch=='A' || ch=='E' || ch=='I' ||
                        ch=='O' || ch=='U');
}

// to count total number of vowel from 0 to n
function countVovels(str,n)
{
    if (n == 1)
        return isVowel(str[n-1]);

    return countVovels(str, n-1) + isVowel(str[n-1]);
}

// Main Calling Function

// string object
let str = "abc de";

// Total numbers of Vowel
document.write(countVovels(str, str.length));

// This code is contributed by shinjanpatra

</script>

Output

2

Time Complexity: O(n), where n is the length of the string
Auxiliary Space: O(n), where n is the length of the string since the function is calling itself n times.

How Recursive Code Working.

This article is contributed by Prakhar Agrawal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.