vslice.cpp

// vslice.cpp -- using valarray slices
#include <iostream>
#include <valarray>
#include <cstdlib>

const int SIZE = 12;
typedef std::valarray<int> vint;
void show(const vint & v, int cols);
int main()
{
	using std::slice;
	using std::cout;
	vint valint(SIZE);

	int i;
	for (i = 0; i < SIZE; ++i) {
		valint[i] = std::rand() % 10;
	}
	cout << "Original array:\n";
	show(valint, 3);
	vint vcol(valint[slice(1,4,3)]);
	cout << "Second column:\n";
	show(vcol, 1);
	vint vrow(valint[slice(3,3,1)]);
	cout << "Second row:\n";
	show(vrow, 3);
	valint[slice(2,4,3)] = 10;
	cout << "Set first column to sum of next two:\n";
	valint[slice(0,4,3)] = vint(valint[slice(1,4,3)])
							+ vint(valint[slice(2,4,3)]);
	show(valint, 3);

	return 0;
}

void show(const vint & v, int cols)
{
	using std::cout;
	using std::endl;

	int lim = v.size();
	for (int i = 0; i < lim; ++i) {
		cout.width(3);
		cout << v[i];
		if (i % cols == cols - 1) {
			cout << endl;
		} else {
			cout << ' ';
		}
		if (lim % cols != 0) {
			cout << endl;
		}
	}
}