How to use the exp, log, and log10 STL functions in Visual C++ (157220)

MORE INFORMATION

Required Header

   <valarray>
   <math>
				

Prototype

   / exp
   template<class T>
   valarray<T> exp(const valarray<T>& x);

   // log
   template<class T>
   valarray<T> log(const valarray<T>& x);

   // log10
   template<class T>
   valarray<T> log10(const valarray<T>& x);
				

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 exp(), log(), and log10() functions through sample code.

Sample Code

////////////////////////////////////////////////////////////////////// 
// 
// Compile options needed: None
// 
// <filename> :  main.cpp
// 
// Functions:
// 
//    exp, log, log10
// 
// Written by Yeong-Kah Tam
// of Microsoft Product Support Services,
// Copyright (c) 1996 Microsoft Corporation. All rights reserved.
////////////////////////////////////////////////////////////////////// 

// disable warning C4267: possible loss of data,
// okay to ignore

#pragma warning(disable: 4267)

#include <iostream>                 // for i/o functions
#include <valarray>                 // for valarray
#include <math.h>                   // for exp(), log(), and log10()

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

#define ARRAY_SIZE  3               // array size

typedef valarray<double> DB_VARRAY;
void main()

{
    int i;
    // Set val_array to contain values 1, 10, 100 for the following test.
    DB_VARRAY val_array(ARRAY_SIZE);
    for (int i = 0; i < ARRAY_SIZE; i++)
        val_array[i] = pow(10.0, i);

    // Display the size of val_array.
    cout << "Size of val_array = " << val_array.size() << "\r\n";

    // Display the content of val_array before calling exp, log, and
    // log10 functions.
    cout << "The values in val_array:\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << val_array[i] << "    ";
    cout << "\r\n\r\n";

    // rvalue_array to hold the return value from calling the sqrt() and
    // pow() functions.
    DB_VARRAY rvalue_array;

    // ----------------------------------------------------------------
    // exp() - display the content of rvalue_array
    // ----------------------------------------------------------------
    rvalue_array = exp(val_array);
    cout << "The result after calling exp():\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << rvalue_array[i] << "     ";
    cout << "\r\n\r\n";

    // ----------------------------------------------------------------
    // log() - display the content of rvalue_array
    // ----------------------------------------------------------------
    rvalue_array = log(val_array);
    cout << "The result after calling log():\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << rvalue_array[i] << "     ";
    cout << "\r\n\r\n";

    // ----------------------------------------------------------------
    // log10() - display the content of rvalue_array
    // ----------------------------------------------------------------
    rvalue_array = log10(val_array);
    cout << "The result after calling log10():\r\n";
    for (i = 0; i < ARRAY_SIZE; i++)
        cout << rvalue_array[i] << "     ";
    cout << "\r\n\r\n";

}
				

Output:

Size of val_array = 3

The values in val_array:

1    10    100

The result after calling exp():

2.71828     22026.5     2.68812e+043

The result after calling log():
0     2.30259     4.60517

The result after calling log10():

0     1     2
				

Note For more information about the pow function in Visual C++ 2005, visit the following Microsoft Developer Network (MSDN) Web site: