Breaking It Down

// Breaking It Down: this program ask for operator (+,-,*,/) then ask for two inputs and does the math
// Renee Waggoner
// June 24, 2019
// Special Requirements: None
package breaking_it_down;
import java.util.Scanner;


public class BreakingItDown {
    // scanner object
    Scanner scan = new Scanner(System.in);
     // Top Level routine for doing a single calculation
    // doCalculation() is method, which returns the boolean value @return if operator is equal to 'q' return false, else true
    boolean doCalculation()
    {
        /**
         * doCalculation() is method, which returns the boolean value
         * @return if operator is equal to 'q' return false, else true
         *
         */
        int operand1, operand2, answer;
        // operator is a variable of char type
        char operator = getOperator();
        // initialize q to quit
        if (operator == 'q')
        {
            return false;
        }
         /**
         * get the value for operand1 if we pass the
         * 1 as argument in getOperand() method
         * if 2 as an argument then getOperand() returns
         * value for operand2
         */
        operand1 = getOperand(1);
        operand2 = getOperand(2);
        // get the final calculated answer after calling doArithmetic() function, which takes three arguments, operator, operand1, operand2
         answer = doArithmetic(operator, operand1, operand2);
         /**
         * Format the result
         * and print on console
         */
        format(operator, operand1, operand2, answer);
        return true;
    } // end of top level routine

    // Get the Operator reliably
    char getOperator()
    {
        char operator = 'q';
        // This next block will get the user desired operator
        // getOperator should contain the following logic
        // condition for loop, if true, loop continues
        boolean operator_is_good = true;
        do {
            System.out.print("Enter an Operator: + - * / q for quit: ");
            String getOperator = scan.nextLine();
            getOperator = getOperator.trim();
            if (getOperator.length() == 0)
            {
                continue; // Need to try this again with no input
            }
            operator = getOperator.charAt(0);
            operator_is_good = false;
            // instructions for what to do with user responses
            switch (operator)
            {
            case 'q':
            case '+':
            case '-':
            case '*':
            case '/':
                operator_is_good = true;
                break;
            default:
                System.out.println("Your operator is bad ... try again:");
                break;
            } // end of switch

        } while (!operator_is_good);
        return operator;
    } // end of char getOperator method

    // get one operand reliably, getOperand method will get the next hunk of logic
    int getOperand(int which)
    {
        which = 2;
        System.out.println("Enter operand " + which);
        // collect the users operand into the "input" variable
        String input;
        boolean operand_is_bad;
        do {
            operand_is_bad = false;

            input = scan.nextLine();
            input = input.trim();
            // if user doesn't enter a value
            if (input.length() == 0)
            {
                operand_is_bad = true;
            }
            for (int i = 0; i < input.length(); i++)
            {   // validate number from string input
                char c = input.charAt(i);
                if (c < '0' || c > '9')
                {
                    // Oops, bad digit
                    operand_is_bad = true;
                    System.out.println("Your last input was bad, try again");
                    scan.close();
                }// end of if statement

            } // end for statement
        } while (operand_is_bad);

        // The following statement will be covered later in the course.
        // For now, just know that it converts a String to an integer
        // Note that Integer.parseInt is picky and blows up with any bad characters
        return Integer.parseInt(input);

    } // end of int getOperand

    // Note: using char because of single character 'q'
    int doArithmetic(char operator, int operand1, int operand2) {
        int answer;
        // Now we have operator, operand1, and operand2.
        // Time to calculate the answer
        // doArithmetic will take the following logic, according to operator
        switch (operator)
        {
        case '+':
            answer = operand1 + operand2;
            break;
        case '-':
            answer = operand1 - operand2;
            break;
        case '*':
            answer = operand1 * operand2;
            break;
        case '/':
            answer = operand1 / operand2;
            break;
        default:
            System.out.println("We shouldn't get here in doArithmentic!!!!");
            answer = -1;
            break;
        } // end of switch
        return answer;
    } // end of int doArithmetic

    // void means no return and then using formatted string using specified arguments
    void format(char operator, int operand1, int operand2, int answer)
    {
        System.out.println(operand1 + " " + operator + " " + operand2 + " = " + answer);
    }
    // We like to keep minimal code in main
    public static void main(String[] args)
    {
        // Construct our class, create BreakingItDown object
        BreakingItDown bid = new BreakingItDown();

        // Call doCalculation for each calculation we are doing, loop until doCalculation() returns true.
        while (bid.doCalculation())
        {
            System.out.println("=======================");
        } // end of while (continue_calculating)

        // prints when user enters 'q'
        System.out.println("Finished Calculations");
    } // end of main
} // end of class BreakItDown