calculator computing multiple numbers

Question

static void Main(string[] args)
{
    string again;
    do
    {
        Console.Write("Enter size to compute: ");
        int size = Convert.ToInt32(Console.ReadLine());
        int[] numbers = new int[size];
        float[] numberS = new float[size];
        Console.Write("Pick one of the operation \"(+) (-) (*) (/)\": ");
        string operation = Console.ReadLine();

        if (operation == "+")
        {
            for (int i = 0; i < size; i++)
            {
                Console.Write("Enter numbers: ");
                numbers[i] = Convert.ToInt32(Console.ReadLine());
            }
            Console.WriteLine("The sum is:" + add(numbers));
        }
        else if (operation == "-")
        {
            for (int i = 0; i < size; i++)
            {
                Console.Write("Enter numbers: ");
                numbers[i] = Convert.ToInt32(Console.ReadLine());
            }
            Console.WriteLine("The subtraction is:" + subtract(numbers));
        }
        else if (operation == "*")
        {
            for (int i = 0; i < size; i++)
            {
                Console.Write("Enter numbers: ");
                numbers[i] = Convert.ToInt32(Console.ReadLine());
            }
            Console.WriteLine("The mulplication is:" + multiply(numbers));
        }
        else if (operation == "/")
        {
            for (int i = 0; i < size; i++)
            {
                Console.Write("Enter numbers: ");
                numberS[i] = Convert.ToInt32(Console.ReadLine());
            }
            Console.WriteLine("The division is:" + division(numberS));
        }
        else Console.WriteLine("Invalid Input");

        Console.Write("Do you want to compute again Y/N: ");
        again = Console.ReadLine().ToUpper();
        Console.Clear();
    } while (again == "Y");
}
static int add(int[] numbers)
{
    int total = 0;
    for (int i = 0; i < numbers.Length; i++)
    {
        total += numbers[i];
    }
    return total;
}
static int subtract(int[] numbers)
{
    int total = 0;
    for (int i = 0; i < numbers.Length; i++)
    {
        total += numbers[i] - numbers[i];
    }
    return total;
}
static int multiply(int[] numbers)
{
    int total = 0;
    for (int i = 0; i < numbers.Length; i++)
    {
        total += numbers[i] * numbers[i];
    }
    return total;
}
static float division(float[] numbers)
{
    float total = 0;
    for (int i = 0; i < numbers.Length; i++)
    {
        total += numbers[i] / numbers[i];
    }
    return total;
}

I was expecting the same results in my phones calculator but no

Answer 1

Your code itself is fine. However your subtract, multiply and division methods are wrong. They are calculating something totally different than intended.

The multiply-method sums the squares of the entered numbers.

The subtract-method always subtracts the current number of itself which equals 0 and always results with a total of 0.

The division method always divides the current number by itself which is 1 and results with a total which equals the number of numbers entered.

Try these methods instead:

static int subtract(int[] numbers)
{
    if (numbers.Length == 0)
        return 0;

    int total = numbers[0];
    for (int i = 1; i < numbers.Length; i++)
    {
        total -= numbers[i];
    }
    return total;
}

static int multiply(int[] numbers)
{
    if (numbers.Length == 0)
        return 0;

    int total = numbers[0];
    for (int i = 1; i < numbers.Length; i++)
    {
        total *= numbers[i];
    }

    return total;
}

static float division(float[] numbers)
{
    if (numbers.Length == 0)
        return 0;

    float total = numbers[0];
    for (int i = 1; i < numbers.Length; i++)
    {
        total /= numbers[i];
    }

    return total;
}

In all of these methods the program first checks if there are any numbers passed. Otherwise it just returns 0.

If there are any numbers you set the first entered number to the total variable because it will be used anyway. The temporary result is always stored in the total variable.

Because the first element is already used the for-loop starts from index 1 instead of 0.

Then the operations are applied to the variable with all remaining numbers.