Microsoft KB Archive/157942

= How to use the STL sqrt function and the STL pow function in Visual C++ =

Article ID: 157942

Article Last Modified on 8/11/2005

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APPLIES TO

 The Standard C++ Library, when used with:  Microsoft Visual C++ 4.2 Enterprise Edition

 Microsoft Visual C++ 5.0 Enterprise Edition

 Microsoft Visual C++ 6.0 Enterprise Edition

 Microsoft Visual C++ 4.2 Professional Edition</li></ul>

 Microsoft Visual C++ 5.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Standard Edition</li></ul>

 Microsoft Visual C++ .NET 2002 Standard Edition</li></ul>

 Microsoft Visual C++ .NET 2003 Standard Edition</li></ul> </li></ul>

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This article was previously published under Q157942

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NOTE: Microsoft Visual C++ NET (2002) supported both the managed code model that is provided by the .NET Framework and the unmanaged native Windows code model. The information in this article applies to unmanaged Visual C++ code only.

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SUMMARY
The sample code below illustrates how to use the STL sqrt and pow functions in Visual C++.

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Prototype
// 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 may 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 <valarrayT>, 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 // // Written by Yeong-Kah Tam // of Microsoft Product Support Services, // Copyright (c) 1996 Microsoft Corporation. All rights reserved. //////////////////////////////////////////////////////////////////////


 * 1) include                // for i/o functions
 * 2) include                // for valarray
 * 3) include                   // for sqrt and pow

using namespace std; // std c++ libs implemented in std #endif
 * 1) if _MSC_VER > 1020  // if VC++ version is > 4.2


 * 1) define ARRAY_SIZE 3               // array size

void main

{

// Set val_array to contain values 1, 4, 9 for the following test valarray 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 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 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
<pre class="fixed_text">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

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