using System;

​

public class Program

{

    // Calculator 1 functions

    public static double increase(double calc1number, double calc1percentage)

    {

        double multiplier = Math.Round(1 + (calc1percentage / 100), 2); 

        Console.WriteLine($"Multiplier used: ×{multiplier}");

        return Math.Round(calc1number * multiplier, 2);

    }

    public static void increaseExplanation(double calc1number, double calc1percentage)

    {

        double newNumber = calc1percentage / 100;

        double multiplier = Math.Round(1 + (calc1percentage / 100), 2);

        double calc1answer = Math.Round(calc1number * multiplier, 2);

        Console.WriteLine($"1. Take {calc1percentage}% and divide it by 100 which gives {newNumber}.\n2. Add 1 to {newNumber} — which represents an increase — to give the multiplier {multiplier}.\n3. Multiply {calc1number} by {multiplier} using a calculator to give the answer {calc1answer}.");

    }

    public static double decrease(double calc1number, double calc1percentage)

    {

        double multiplier = Math.Round(1 - (calc1percentage / 100), 2);

        Console.WriteLine($"Multiplier used: ×{multiplier}");

        return Math.Round(calc1number * multiplier, 2);

    }

    public static void decreaseExplanation(double calc1number, double calc1percentage)

    {

        double newNumber = calc1percentage / 100;

        double multiplier = Math.Round(1 - (calc1percentage / 100), 2);

        double calc1answer = Math.Round(calc1number * multiplier, 2);

        Console.WriteLine($"1. Take {calc1percentage}% and divide it by 100 which gives {newNumber}.\n2. Minus {newNumber} from 1 — which represents a decrease — to give the multiplier {multiplier}.\n3. Multiply {calc1number} by {multiplier} using a calculator to give the answer {calc1answer}.");

    }

​

    // Calculator 2 functions

    public static double function1(double number1, double number2)

    {

        return Math.Round((number1 / number2) * 100, 2);

    }

​

    public static double function2(double number1, double number2)

    {

        return Math.Round((number2 / number1) * 100, 2);

    }

    // Calculator 3 functions

    public static double simple(double calc3number, double calc3percentage, double calc3years)

    {

        double interest = Math.Round(calc3number * (calc3percentage / 100) * calc3years, 2);

        Console.WriteLine($"Interest: £{interest}");

        return calc3number + interest;

    }

    public static double compound(double calc3number, double calc3percentage, double calc3years, int calc3times)

    {

        double interest = Math.Round(calc3number * (Math.Pow(1 + ((calc3percentage / 100) / calc3times), calc3times * calc3years)), 2);

        Console.WriteLine($"Interest: £{interest}");

        return calc3number + interest;

    }

​

        public static void Main()

        {

        // Calculator 1 variables

        double calc1number;

        double calc1percentage;

        string calc1function;

        double calc1answer;

        string calc1explanation;

        // Calculator 2 variables

        double calc2number1;

        double calc2number2;

        double calc2answer1;

        double calc2answer2;

        // Calculator 3 variables

        double calc3number;

        double calc3percentage;

        double calc3years;

        string calc3years2;

        int calc3times;

        string calc3function;

        double calc3answer;

​

        // Using a switch statement to choose which calculator to use

        Console.WriteLine("Welcome to Percentage Calculator.");

        modeInput:

        Console.WriteLine("\nType '1' for percentage increase/decrease calculator.\nType ‘2’ to find out what percentage two numbers are of each other.\nType '3' for interest calculator.");

        int mode = Int32.Parse(Console.ReadLine());

        if (mode != 1 && mode != 2 && mode != 3)

        {

            Console.WriteLine("Please try again.");

            goto modeInput;

        }

        switch(mode)

        {

            // Calculator 1

            case 1:

                // Asking for the original number

                Console.WriteLine("Please enter the number you'd like to increase/decrease by a percentage amount.");

                calc1numberInput:

                try

                {

                    calc1number = Convert.ToDouble(Console.ReadLine());

                }

                catch

                {

                    Console.WriteLine("Please enter a valid number.");

                    goto calc1numberInput;

                }

​

                // Asking for the percentage

                Console.WriteLine("Now please enter the percentage you'd like to increase/decrease your number by.");

                calc1percentageInput:

                try

                {

                    calc1percentage = Convert.ToDouble(Console.ReadLine());

                }

                catch

                {

                    Console.WriteLine("Please enter numbers only.");

                    goto calc1percentageInput;

                }

​

                // Checking which function to use + getting the answer from the function

                Console.WriteLine("Would you like to increase or decrease your number by the percentage amount? Type '+' for increase and '-' for decrease.");

                calc1functionInput:

                calc1function = Console.ReadLine();

                if (calc1function == "+")

                {

                    calc1answer = increase(calc1number, calc1percentage);

                    Console.WriteLine($"Answer is: {calc1answer}");

                    // Asking if the user would like an explanation for the answer

                    calc1explanationInput:

                    Console.WriteLine("Would you like an explanation for the answer? Type 'Y' for yes and 'N' for no.");

                    calc1explanation = Console.ReadLine();

                    if (calc1explanation == "Y" || calc1explanation == "y")

                    {

                        increaseExplanation(calc1number, calc1percentage);

                        goto modeInput;

                    }

                    else if (calc1explanation == "N" || calc1explanation == "n")

                    {

                        // Looping the program

                        goto modeInput;

                    }

                    else

                    {

                        Console.WriteLine("Please try again.");

                        goto calc1explanationInput;

                    }

                }

                else if (calc1function == "-")

                {

                    calc1answer = decrease(calc1number, calc1percentage);

                    Console.WriteLine($"Answer is: {calc1answer}");

                    // Asking if the user would like an explanation for the answer

                    calc1explanationInput:

                    Console.WriteLine("Would you like an explanation for the answer? Type 'Y' for yes and 'N' for no.");

                    calc1explanation = Console.ReadLine();

                    if (calc1explanation == "Y" || calc1explanation == "y")

                    {

                        decreaseExplanation(calc1number, calc1percentage);

                        goto modeInput;

                    }

                    else if (calc1explanation == "N" || calc1explanation == "n")

                    {

                        // Looping the program

                        goto modeInput;

                    }

                    else

                    {

                        Console.WriteLine("Please try again.");

                        goto calc1explanationInput;

                    }

                }

                else

                {

                    Console.WriteLine("Please try again.");

                    goto calc1functionInput;

                }

            // Calculator 2

            case 2:

                // Asking for the first number

                Console.WriteLine("Please enter a number.");

                calc2number1Input:

                try

                {

                    calc2number1 = Convert.ToDouble(Console.ReadLine());

                }

                catch

                {

                    Console.WriteLine("Please enter a valid number.");

                    goto calc2number1Input;

                }

​

                // Asking for the second number

                Console.WriteLine("Now please enter the second number.");

                calc2number2Input:

                try

                {

                    calc2number2 = Convert.ToDouble(Console.ReadLine());

                }

                catch

                {

                    Console.WriteLine("Please enter numbers only.");

                    goto calc2number2Input;

                }

​

                // Getting the answers from the functions

                calc2answer1 = function1(calc2number1, calc2number2);

                calc2answer2 = function2(calc2number1, calc2number2);

                Console.WriteLine($"{calc2number1} is {calc2answer1}% of {calc2number2}.\n{calc2number2} is {calc2answer2}% of {calc2number1}.");

​

                // Looping program

                goto modeInput;

            // Calculator 3

            case 3:

                // Asking for the original amount of money

                Console.WriteLine("Please enter the original amount.");

                calc3numberInput:

                try

                {

                    calc3number = Convert.ToDouble(Console.ReadLine());

                }

                catch

                {

                    Console.WriteLine("Please enter a valid number.");

                    goto calc3numberInput;

                }

​

                // Asking for the interest percentage

                Console.WriteLine("Now please enter the interest percentage.");

                calc3percentageInput:

                try

                {

                    calc3percentage = Convert.ToDouble(Console.ReadLine());

                }

                catch

                {

                    Console.WriteLine("Please enter numbers only.");

                    goto calc3percentageInput;

                }

                // Asking for the amount of years of interest

                Console.WriteLine("Now please enter after how many years you'd like to know the new value.");

                calc3yearsInput:

                try

                {

                    calc3years = Convert.ToDouble(Console.ReadLine());

                }

                catch

                {

                    Console.WriteLine("Please enter numbers only.");

                    goto calc3yearsInput;

                }

                if (calc3years <= 0)

                    {

                        Console.WriteLine("You can not have a negative amount of years. Try again.");

                        goto calc3yearsInput;

                    }

                    else if (calc3years > 1)

                    {

                        calc3years2 = "years";

                    }

                    else

                    {

                        calc3years2 = "year";

                    }

                // Checking which function to use + getting the answer from the function

                Console.WriteLine("Type 's' for simple interest or 'c' for compound interest.");

                calc3functionInput:

                calc3function = Console.ReadLine();

                if (calc3function == "s")

                {

                    calc3answer = simple(calc3number, calc3percentage, calc3years);

                    Console.WriteLine($"The total amount after {calc3years} {calc3years2} at {calc3percentage}% simple interest is £{calc3answer}.");

                }

                else if (calc3function == "c")

                {

                    Console.WriteLine("How many times is the interest rate compounded per year?");

                    calc3timesInput:

                    try

                    {

                        calc3times = Convert.ToInt32(Console.ReadLine());

                    }

                    catch

                    {

                        Console.WriteLine("Please enter numbers only.");

                        goto calc3timesInput;

                    }

                    calc3answer = compound(calc3number, calc3percentage, calc3years, calc3times);

                    Console.WriteLine($"The total amount after {calc3years} {calc3years2} at {calc3percentage}% compound interest is £{calc3answer}.");

                }

                else

                {

                    Console.WriteLine("Please try again.");

                    goto calc3functionInput;

                }

                // Looping the program

                goto modeInput;

        }

    }

}