// Definitions for IO
#include <cmath>
#include <iostream>
using namespace std;

// Here are the prototypes for our procedures 
void   sum_array(double[], double &, int);
double ddot(double[], double[], int);

int main()
{
	int             k, n, in;
	double          a[100], b[100], sum;
	// Arrays are indexed from 0,  a[0], ..., a[99] 

	n = 100;
        // endl is newline
	cout << "Type a value for in: " << endl;
	cin  >> in;

	cout << "This is how you write: in = " << in << endl;

	for (k = 0; k < n; k++) {	// for k = 0, ..., n-1 
		a[k] = k + 1;	// k++ means k = k + 1 
		b[k] = -sin(double(k + 1));
	}

	// Compute the inner product between a and b. 
	cout << "The inner product is " << ddot(a, b, n) << endl;

	// Arrays are passed by reference automatically.
        // Use a reference parameter for sum.

	sum_array(a, sum, n);

	cout << "The sum of the array is " << sum << endl;

        return 0; // Return status to unix
}

void sum_array(double a[], double &sum, int n)
// void, i.e. not a function. double &sum means that we can return
// a value in sum (call by reference)
{
	int             k;	// k is local to sum_array 

	sum = 0;

	for (k = 0; k < n; k++)
		sum += a[k];	// i.e. sum = sum + a[k] 
}

// NOT void here since this is a function (of type double) returning a
// result.
double ddot(double x[], double y[], int n)
{
	int             k;
	double          sum;

	sum = 0.0;
	for (k = 0; k < n; k++)
		sum += x[k] * y[k];

	return sum;		// return the result
}