Manipulate the value in a valarray : valarray subscript indexer « valarray « C++ Tutorial

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2. valarray
3. valarray subscript indexer

/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>
#include <valarray>
using namespace std;

// print valarray
template <class T>
void printValarray (const valarray<T>& va)
{
    for (int i=0; i<va.size(); i++) {
        cout << va[i] << ' ';
    }
    cout << endl;
}

int main()
{
    // create and initialize valarray with nine elements
    valarray<double> va(9);
    for (int i=0; i<va.size(); i++) {
        va[i] = i * 1.1;
    }

    // print valarray
    printValarray(va);

    // double values in the valarray
    va *= 2.0;

    // print valarray again
    printValarray(va);

    // create second valarray initialized by the values of the first plus 10
    valarray<double> vb(va+10.0);

    // print second valarray
    printValarray(vb);

    // create third valarray as a result of processing both existing valarrays

    valarray<double> vc;
    vc = sqrt(va) + vb/2.0 - 1.0;
    
    // print third valarray
    printValarray(vc);
}

0 1.1 2.2 3.3 4.4 5.5 6.6 7.7 8.8
0 2.2 4.4 6.6 8.8 11 13.2 15.4 17.6
10 12.2 14.4 16.6 18.8 21 23.2 25.4 27.6