Mega Code Archive
Print valarray as two-dimensional array
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/* 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 as two-dimensional array
template<class 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()
{
// create valarray for 12 elements
valarray<double> va(12);
// initialize valarray by values 1.01, 2.02, ... 12.12
for (int i=0; i<12; i++) {
va[i] = (i+1) * 1.01;
}
printValarray(va,4);
/* create array of indexes
* - note: element type has to be size_t
*/
valarray<size_t> idx(4);
idx[0] = 8;
idx[1] = 0;
idx[2] = 3;
idx[3] = 7;
// use array of indexes to print the ninth, first, fourth, and eighth elements
printValarray(valarray<double>(va[idx]), 4);
// change the first and fourth elements and print them again indirectly
va[0] = 11.11;
va[3] = 44.44;
printValarray(valarray<double>(va[idx]), 4);
// now select the second, third, sixth, and ninth elements
// and assign 99 to them
idx[0] = 1;
idx[1] = 2;
idx[2] = 5;
idx[3] = 8;
va[idx] = 99;
// print the whole valarray again
printValarray (va, 4);
}
/*
1.01 2.02 3.03 4.04
5.05 6.06 7.07 8.08
9.09 10.1 11.11 12.12
9.09 1.01 4.04 8.08
9.09 11.11 44.44 8.08
11.11 99 99 44.44
5.05 99 7.07 8.08
99 10.1 11.11 12.12
*/
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