Program firstvowel.cs

Demonstrates usage of the String.Substring() and String.IndexOf() methods 

using System;

 * Written by Bryan Miller on March 30, 2007
 * or

class Program {

    static void Main(string[] args) {

        string vowels = "AEIOUaeiou"; //the vowels
        string currentLetter = string.Empty; //the character we're currently examining in the word
        string word = string.Empty; //the word entered by the user

        int wordlen = -1; //will hold length of word entered by user
        int index = -1; //will hold value corresponding to current position that we're evaluating within the word

        Console.WriteLine("For our purposes, \"Y\" is not considered among the vowels...\n");

        //unless and until user enters the word "quit", do all this...

        do {

            //ensure that user enters a string of characters whose length is between 3 and 15, inclusive
            do {
                Console.WriteLine("Please enter a word that is 3 to 15 characters long, ");
                Console.Write("or enter \"quit\" to exit program: ");
                word = Console.ReadLine().Trim();
                wordlen = word.Length;


                if (wordlen < 3) { Console.WriteLine("Your word should be at least 3 characters in length.\n"); } //end if
                if (wordlen > 15) { Console.WriteLine("Your word should be no more than 15 characters in length.\n"); } //end if

            } while ((wordlen < 3) || (wordlen > 15)); //end do-while

             * The following for loop steps through the individual letters of the word entered by the user, beginning with the
             * first letter of that word and, if necessary, going all the way to the last letter.  For each letter in the word,
             * we use the .IndexOf String instance method to determine if that letter is a vowel or not.  If it IS, we set our
             * integer variable named index equal to i, and since i is the index of the current letter we're examining, index 
             * will -- as we break out of the for loop -- hold the index at which the first vowel occurs in the word.  We could
             * have completed the for loop, stepping through each and every element of the word.  But if the first vowel doesn't
             * occur at the very last position in the word, it would be inefficient.  Better to break out of the for loop as soon
             * as we have located the very first vowel.

            for (int i = 0; i < wordlen; i++) {
                currentLetter = word.Substring(i, 1);
                index = vowels.IndexOf(currentLetter);
                if (index != -1) {
                    index = i;
                }//end if
            }//end for loop

            /* if the word the user entered is "quit", then user wants to exit program and isn't interested in the information
             * contained in the following Console.WriteLine() invocations */

            if (word != "quit") {
                if (index != -1) {
                    Console.WriteLine("The first vowel, \"{0}\", occurred at position {1} in \"{2}\"", currentLetter, index, word);
                    Console.WriteLine("It is the {0}", PositionOfLetter(index,wordlen));
                } else {
                    Console.WriteLine("There were no vowels found, therefore the string you entered");
                    Console.WriteLine("cannot properly be called a word.");
                }//end if
            }//end if


        } while (word.ToLower() != "quit"); //end outer do-while

    }//end Main

    private static string PositionOfLetter(int index, int wordlen) {

         * The 0th position is the word is the 1st character.  The 4th position is the 5th character, etc.
         * This switch statement maps this relationship, and allows us to build up the returnVal string as
         * a return value, making this private static method useful to the program's output

        string returnVal = string.Empty;

        switch (index) {

            case 0:
                returnVal = "1st";

            case 1:
                returnVal ="2nd";

            case 2:
                returnVal ="3rd"; 

            case 3:
                returnVal ="4th"; 

            case 4:
                returnVal = "5th";

            case 5:
                returnVal = "6th";

            case 6:
                returnVal ="7th";

            case 7:
                returnVal ="8th";

            case 8:
                returnVal ="9th";

            case 9:
                returnVal ="10th";

            case 10:
                returnVal ="11th";

            case 11:
                returnVal ="12th";

            case 12:
                returnVal = "13th";

            case 13:
                returnVal ="14th";

            case 14:
                returnVal ="last";

                returnVal ="unknown error in switch statement";

        }//end switch

        returnVal += " of " + wordlen.ToString() + " characters in the word";
        return returnVal;
    }//end private static string method

}//end class Program