Issues with looping code and do-while loops (c#)

Question

static double calculateTotals(double a)
    {
        double transfee = a * .01;
        double total = a + transfee;
        return total;
    }

    static void Main(string[] args)
    {
        Console.WriteLine("How many dontations to process?");
        int donations = Convert.ToInt16(Console.ReadLine());
        int[] count = new int[] { donations + 1 };
        int ct = 1;
        int i = -1;
        do
        {
            Console.WriteLine("Enter name: ");
            string name = Console.ReadLine();
            Console.WriteLine("Enter donation amount: ");
            double amount = Convert.ToDouble(Console.ReadLine());
            double transfee = amount * .01;
            i++;
            ct = count[i += 1];
            Console.WriteLine(name + "\t" + amount + "\t" + transfee);
        } while (i < donations);
        Console.WriteLine("TOTALS:" + "\t" + calculateTotals(amount) + "\t" + transfee);
        Console.ReadLine();
    }
}

Hello. I am a beginner at coding, so I apologize if this is a poor attempt.

I am trying to make an app that records the amount donated by an individual, calculates a transaction fee, and outputs the results for each person. At the end, I am creating a final row of output that will state the total donations and the total transaction fees.

I am currently unsure how to properly implement the array into my loop, and am unsure if the loop is optimized in general.

Again, I am a beginner. I apologize for such code, but I'd love some clarification on these things.

Thank you!

Answer 1

First, your array declaration syntax is wrong. See this link .

So it should be int[] count = new int[donations+1];

Second, you need to declare and instantiate your amount and transfee variables outside of your loop.

        double transfee = 0.0F;
        double amount = 0.0F;
        do
        {
            ...
            amount = Convert.ToDouble(Console.ReadLine());
            transfee = amount * .01;
            ...
        } while (i < donations);

This should be enough information to get you going again. Since you're learning, I don't think anyone would really unfold an answer for you that does the job you're trying to figure out :)

Answer 2

Your code :

        int i = -1;

        do
        {
            ...

            i++;
            ct = count[i += 1];
            ...

        } while (i < donations);

You are actually increase i two times , then get values from count[i] assign to ct variable

See this sample :

        int[] count = new int[3];
        count[0] = 0;
        count[1] = 1;
        count[2] = 2;

        int i = -1;
        do
        {
            i++;
            int x = count[i += 1];
            Console.WriteLine(x);
        } while (i < 3);

It will cause IndexOutOfRangeException

Explain :

First Loop :

i++;                   // i increased 1, so i = 0
int x = count[i += 1]; // i increased 1, so i = 1, then get count[1] assign to x, x is 1

Second loop:

i++;                   // i increased 1, so i = 2
int x = count[i += 1]; // i increased 1, so i = 3, then get count[3] assign to x

count[3] cause IndexOutOfRangeException

Something like count[i += 1] will make your code more difficult to maintain, in my opinion, you should avoid it if possible, try to write it explicity as you can