exp, log, and log10 (Sample)

The sample code below illustrates how to use the exp, log, and log10 STL functions in Visual C++.

Required Header:
<valarray>

 // 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 do not match the version in the header file. Some have been modified to improve readability.

Description:
This article illustrates the use of the STL exp(), log(), and log10() functions through sample code.

Sample Code:

//////////////////////////////////////////////////////////////////////
//
// Compile options needed: None
//
// <filename> :  main.cpp
//
// Functions:
//
//    exp, log, log10
//////////////////////////////////////////////////////////////////////

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

using namespace std;


#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.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";
}

 

Program Output is:

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