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My array max size is 20. If I were to enter data that would be less than 20,how do I get it where my program only counts the used arrays?

for (int i = 0; i < Score.Length; i++)

 sum = sum + Score[i];


average = sum / Score.Length;

If I use this for loop above, it always divides by 20 for the average. I need it to only count the ones I entered, not 20. I would prefer solutions using arrays

If you insist in using arrays, then you must keep track of how many items you added to the array, like:

int[] Score = new int[20];
Random rdn = new Random();

int size=0;
for(int i=0;i<rdn.Next(0,20);i++)

 Score[i] = rdn.Next();
 size++;


int sum = 0;

for (int i = 0; i < size; i++)

 sum = sum + Score[i];


double average = sum / size;

A better option is to use the List class that keep track for you of the number of items you add

List<int> Score = new List<int>();
Random rdn = new Random();


for(int i=0;i<rdn.Next(0,20);i++)

 Score.Add(rdn.Next());


int sum = 0;

for (int i = 0; i < Score.Count; i++)

 sum = sum + Score[i];

double average = sum / Score.Count;

And of course, as you didn't say the type of your data you could use other data types, like double, float, long, decimal for both solutions.

That is probably an overkill, but another approach would be to use a SparseVector class of the Math.Numerics package:

Sparse Vector uses two arrays which are usually much shorter than the vector. One array stores all values that are not zero, the other stores their indices.

PM > Install-Package MathNet.Numerics

var vector = SparseVector.Build.SparseOfArray(Score);
var sum = vector.Sum();

Sum() will only go through non-empty elements.

You need to keep track of the record that are != 0, so

int count = 0;
for(int i = 0; i < array.Length; i++)

 if ( array[i] != 0 ) 
 
 count++;
 sum += array[i];
 

average = sum / count;

And beware of division by 0 ;)