Help with basic arrays

[EternalTactician]

We just stared with arrays today and i have a hard time understanding them. I am trying to implement arrays into a program i already did before, the program finds the average of 3 grades and gives a letter grade too. I need to implement the arrays to find 10 grades and a letter grade too.

Here is my code

using namespace std;

const int N=10;


double math(int test1, int test2, int test3){
    return double(test1+test2+test3)/3.0;
}
void output (double avg1, char lg){
    cout<<"Your average is: "<< avg1;
    cout<<" You made a: "<< lg;
}

void input(int division, int){

{

      int array[N];          //Declaring array
      int sum=0;
      for(int i=0;i<N;i++)   //Loop which inputs arrays data and
                                //Calculates its sum
      {
              cout<<"Enter test "<<i+1<<endl;
              cin>>array[i];
              sum=sum+array[i];
      }
      //Now calling division function to find the sum...

      cout<<"Average of array elements is "<<division(sum,N);
    return double(average)/3.0; (int sum,int N);


}

}



char lettergrade (double average)
{
    if (average>=93){
        return 'A';
    }
    else if ((85<= average)&&(average <=93)){
        return 'B';
    }
    else if ((76<= average)&&(average <=85)){
        return 'C';
    }
    else if ((70<= average)&&(average <=76)){
        return 'D';
    }
    else if ((0<= average)&&(average <=70)){
        return 'F';
    }
}

int main()
{
    int grade1;
    int grade2;
    int grade3;
    double average;
    char let;
    cout<<"Enter grade 1:"<<endl;
    cin>>grade1;
    cout<<"Enter grade 2:"<<endl;
    cin>>grade2;
    cout<<"Enter grade 3:"<<endl;
    cin>>grade3;
    average = math(grade1, grade2, grade3);
    let = lettergrade(average);
    output (average, let);
    return 0;
}