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