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

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);
				

Description

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";

}
				

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