STL Sample for the exp, log, and log10 Functions

ID: Q157220

The information in this article applies to:

SUMMARY

The sample code below illustrates 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);
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.
////////////////////////////////////////////////////////////////////// 

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

#define ARRAY_SIZE  3               // array size
typedef valarray<double> DB_VARRAY; 

void main()
{ 
    // 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, i);

    // Display the size of val_array.
    cout << "Size of val_array = " << val_array.length() << "\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

REFERENCES

Visual C++ Books On Line: Visual C++ Books:C/C++:Standard C++ Library Reference.

Additional query words: STL STLSample exp log log10 

Keywords          : kbcode STLIss 
Version           : WINNT:4.2;
Platform          : NT WINDOWS
Issue type        : kbhowto

Last Reviewed: October 10, 1997