The following code example is taken from the book
The C++ Standard Library - A Tutorial and Reference, 2nd Edition
by Nicolai M. Josuttis, Addison Wesley Longman, 2012
Copyright © 2012 by Pearson Education, Inc. and Nicolai M. Josuttis
#include <iostream>
#include <valarray>
using namespace std;
// print valarray line-by-line
template <typename T>
void printValarray (const valarray<T>& va, int num)
{
for (int i=0; i<va.size()/num; ++i) {
for (int j=0; j<num; ++j) {
cout << va[i*num+j] << ' ';
}
cout << endl;
}
cout << endl;
}
int main()
{
// valarray with 12 elements
// - four rows
// - three columns
valarray<double> va(12);
// fill valarray with values
for (int i=0; i<12; i++) {
va[i] = i;
}
printValarray (va, 3);
// assign 77 to all values that are less than 5
va[va<5.0] = 77.0;
// add 100 to all values that are greater than 5 and less than 9
va[va>5.0 && va<9.0]
= valarray<double>(va[va>5.0 && va<9.0]) + 100.0;
printValarray (va, 3);
}