The sample code below illustrates how to use the sqrt
and pow
STL functions in Visual C++.
Required Header:
<valarray>
// sqrt
template<class T>
inline valarray<T> sqrt(const valarray<T>& x);
// pow
template<class T>
inline valarray<T> pow(const valarray<T>& x, const valarray<T>& y);
template<class T>
inline valarray<T> pow(const valarray<T> x, const T& y);
template<class T>
inline valarray<T> pow(const T& x, const valarray<T>& y);
Note: The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
Description:
This article illustrates the use of STL sqrt() and pow() functions through sample code. sqrt() returns an object of class valarray<T>, each of whose elements at index I is the square root of x[I]. pow() has three template functions. The first template function returns an object of class valarray<T>, each of whose elements at index I is x[I] raised to the power of y[I]. The second template function stores in element I x[I] raised to the power of y. The third template function stores in element I x raised to the power of y[I].
Sample Code:
//////////////////////////////////////////////////////////////////////
//
// Compile options needed: /GX
//
// main.cpp : Illustrates the use of STL sqrt() and pow() functions.
//
// Functions:
//
// sqrt, pow
//////////////////////////////////////////////////////////////////////
#include <iostream> // for i/o functions
#include <valarray> // for valarray
#include <cmath> // for sqrt() and pow()
using namespace std ;
#define ARRAY_SIZE 3 // array size
void main()
{
// Set val_array to contain values 1, 4, 9 for the following test
valarray<double> val_array(ARRAY_SIZE);
for (int i = 0; i < ARRAY_SIZE; i++)
val_array[i] = (i+1) * (i+1);
// Display the size of val_array
cout << "Size of val_array = " << val_array.size() << endl;
// Display the values of val_array before calling sqrt() and pow().
cout << "The values in val_array:" << endl;
for (i = 0; i < ARRAY_SIZE; i++)
cout << val_array[i] << " ";
cout << endl << endl;
// Initialize rev_valarray that is the reverse of val_array.
valarray<double> rev_valarray(ARRAY_SIZE);
for (i = 0; i < ARRAY_SIZE; i++)
rev_valarray[i] = val_array[ARRAY_SIZE - i - 1];
// Display the size of rev_valarray.
cout << "Size of rev_valarray = " << rev_valarray.size() << endl;
// Display the values of rev_valarray.
cout << "The values in rev_valarray:" << endl;
for (i = 0; i < ARRAY_SIZE; i++)
cout << rev_valarray[i] << " ";
cout << endl << endl;
// rvalue_array to hold the return value from calling the sqrt() and
// pow() functions.
valarray<double> rvalue_array;
// ----------------------------------------------------------------
// sqrt() - display the content of rvalue_array
// ----------------------------------------------------------------
// Display the result of val_array after calling sqrt().
rvalue_array = sqrt(val_array);
cout << "The result of val_array after calling sqrt():" << endl;
for (i = 0; i < ARRAY_SIZE; i++)
cout << rvalue_array[i] << " ";
cout << endl << endl;
// ----------------------------------------------------------------
// pow() - display the content of rvalue_array
// ----------------------------------------------------------------
// This template function returns an object of class valarray<T>,
// each of whose elements at I is x[I] raised to the power of y[I].
rvalue_array = pow(val_array, rev_valarray);
cout << "The result after calling pow(val_array, rev_valarray):"
<< endl;
for (i = 0; i < ARRAY_SIZE; i++)
cout << rvalue_array[i] << " ";
cout << endl << endl;
// This template function stores in element I x[I] raised to the
// power of y, where y=2.0.
rvalue_array = pow(val_array, 2.0);
cout << "The result after calling pow(val_array, 2.0):" << endl;
for (i = 0; i < ARRAY_SIZE; i++)
cout << rvalue_array[i] << " ";
cout << endl << endl;
// This template function stores in element I x raised to the
// y[I] power, where x=2.0.
rvalue_array = pow(2.0, val_array);
cout << "The result after calling pow(2.0, val_array):" << endl;
for (i = 0; i < ARRAY_SIZE; i++)
cout << rvalue_array[i] << " ";
cout << endl << endl;
}
Program Output is:
Size of val_array = 3
The values in val_array:
1 4 9
Size of rev_valarray = 3
The values in rev_valarray:
9 4 1
The result of val_array after calling sqrt():
1 2 3
The result after calling pow(val_array, rev_valarray):
1 256 9
The result after calling pow(val_array, 2.0):
1 16 81
The result after calling pow(2.0, val_array):
2 16 512