C#: Check whether the first appearance of 'a' in a given string is immediately followed by another 'a'

Last update on June 25 2025 13:04:01 (UTC/GMT +8 hours)

First 'a' Followed by Another 'a'

Write a C# Sharp program to check whether the first appearance of "a" in a given string is immediately followed by another "a".

Visual Presentation:

C# Sharp: Basic Algorithm Exercises - Check if the first appearance of "a" in a given string is immediately followed by another 'a'.

Sample Solution:-

C# Sharp Code:

using System;

// Namespace declaration
namespace exercises
{
    // Class declaration
    class Program
    {
        // Main method - entry point of the program
        static void Main(string[] args)
        {
            // Displaying the output of the 'test' method with different string inputs
            Console.WriteLine(test("caabb"));    // Output: False
            Console.WriteLine(test("babaaba"));  // Output: True
            Console.WriteLine(test("aaaaa"));    // Output: False
            Console.ReadLine();  // Keeping the console window open
        }

        // Method to check for the presence of "aa" in the string within the first two occurrences of 'a'
        public static bool test(string str)
        {
            var counter = 0;  // Counter to track occurrences of 'a' in the string

            // Loop through the characters of the string except for the last character
            for (var i = 0; i < str.Length - 1; i++)
            {
                if (str[i].Equals('a'))  // Check if the character at index 'i' is 'a'
                {
                    counter++;  // Increment the counter for each occurrence of 'a'
                }

                // Check if the current and next characters form the substring "aa" and the 'a' occurrences are less than 2
                if (str.Substring(i, 2).Equals("aa") && counter < 2) 
                {
                    return true;  // Returns true if "aa" is found within the first two 'a's
                }
            }

            return false;  // Returns false if "aa" is not found within the first two 'a's
        }
    }
}

Sample Output:

True
False
True

Flowchart:

For more Practice: Solve these Related Problems:

Write a C# program to check whether the first 'a' in the string is followed by another 'a' within the next 2 characters.
Write a C# program to verify if every 'a' in a string is immediately followed by another 'a'.
Write a C# program to check if the first occurrence of 'a' is followed by 'b' and then another 'a'.
Write a C# program to determine if the string starts with a double 'a' and ends with a double 'a'.

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