How would you calculate the sum of the first and last values in an array.

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Hi there,

Please provide a solution to calculating the first and last number in an array. like below.

So I have an array:
133286

I want to calculate the sum until I have only two numbers like so:

Thanks in Advance.

What I have tried:

I have tried using a for loop but it only runs once, how do I continuously run it till i have only two digits.

C#

int[] per = new int[1000];
            int sum = 0;
            Console.WriteLine("The % score:");
            for (int i = 0; i < count; i++)
            {
                per[i] = numbers[i] + numbers[count-1];
                count--;
                sum++;
                
                
            }

Posted 4-Oct-21 1:10am

CoderL18

Updated 4-Oct-21 6:30am

PIEBALDconsult

v2

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Richard MacCutchan 4-Oct-21 7:24am

You need to adjust the end point of the array each time. So as you add the last number to the first you reduce the end point of the array by 1. So at the end of each loop the number of elements in the array will be something around half of the original. But you need to decide how many digits should remain as the final value, so you know when to stop the loop.

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OriginalGriff · Answer 1 · 2021-10-04T01:24:00

Rephrasing your question so it's more obvious:

133286
First = 1, last = 6: Sum = 7
Remaining
 3328
First = 3, last = 8: Sum = 11
Remaining
  32
First = 3, last = 2: Sum = 5

And it's clear that this is the same task repeated - so make your code reflect that.

The first thing to do is to put the code to work out the sums into a method, so you can call it repeatedly. Pass it the array and the start index, have it return the sum, and it's pretty simple to do.

When you have that working, add your loop to call it repeatedly.
Start by making that call the array the right number of times - sort out when the loop should exit first, and do something useful with the result your method return. What exactly is "useful" will depend on you, the environment yoru code is to run in, and what exactly you want to do with the result.
For example, a Console app may want to print each result, but a more general app may want to add them to a collection (a List or an Array maybe) for later processing. We don't know what your tutor wants you to do!

Then make it pass an incrementing start index to method, and you're done.

Think about the task, try it on paper, and you'll get it done in very little time.

Richard MacCutchan · Answer 2 · 2021-10-04T01:52:00

Something like this, but probably needs refining:

C#

int start = 0;
int end = numbers.Length - 1;
while (end > 1)
{
    for (start = 0; start < end ; start++, end--)
    {
        Console.Write($"start: {start}, end: {end}");
        numbers[start] += numbers[end];
        Console.WriteLine($" numbers[start] += numbers[end]: {numbers[start]}");
        numbers[end] = 0;
    }
    Console.WriteLine($"start: {start}, end: {end}");

    for (int i = 0; i < 9 ; i++)
    {
        Console.Write($"{numbers[i]}, ");
    }
    Console.WriteLine("");
}

How would you calculate the sum of the first and last values in an array.

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