functions, exercise 01, slide 34

package class170703;

public class functions01 {
    // Functions, exercise 01, slide 34
    // input: array of numbers and a digit
    // output: number of appearances of the digit in the array numbers

    // building a data sample: array of integers and a digit.
    // then calling function countAppearances to calculate appearances
    // and print results
    public static void main(String[] args) {
        // create a sample data for testing only
        // array of integers
        int[] numbersArray = { 144, 47, 42, 74, 19 };
        // a digit
        int aDigit = 4;

        // printing a message containing array elements and the digit
        System.out.printf("searching for %d in %s\n", aDigit,
                toString(numbersArray));

        // count and print appearances of the digit in the array values
        System.out.printf("%d appears %d times\n", aDigit,
                countAppearances(numbersArray, aDigit));

    }

    // convert an array of integer numbers to a string
    // input: an array of integer values
    // output: a string with all values from the array separated by comma
    public static String toString(int[] array) {
        // if array is empty
        if (array.length == 0) {
            // return result and quit
            return "[]";
        }

        // building a string from all numbers in the array
        String result = "" + array[0]; // start with the first number

        // scan the numbers in the array without the first
        for (int i = 1; i < array.length; i += 1) {
            // convert number to string and add it to the result string
            result += ", " + array[i];
        }

        // return the result surrounded by brackets
        return "[" + result + "]";
    }

    // count the appearances of a digit in an array of integers
    // input: an array of integer values and a digit
    // output: number of times the digit appears in the values of the array
    public static int countAppearances(int[] numbersArray, int digit) {
        // initialize a counter
        int counter = 0;

        // for each number in the array
        for (int aNumber : numbersArray) {
            // count appearances of digit in it and update counter
            counter += countAppearance(aNumber, digit);
        }

        return counter;
    }

    // count the appearances of a digit in an integer number
    // input:an integer number and a digit
    // output: number of times the given digit appears in the given number
    public static int countAppearance(int number, int digit) {
        // initialize a counter
        int count = 0;

        // loop to scan each digit in the number
        do {
            // update counter by one iff most right digit is equal to digit
            count += number % 10 == digit ? 1 : 0;
            // drop the most right digit
            number /= 10;
        } while (number > 0); // loop while number has more digits to check

        // return the result
        return count;
    }

}