exp, log, and log10
Illustrates how to use the exp, log, and log10 Standard Template Library (STL) functions in Visual C++.
template<class T>
valarray<T> exp(
const valarray<T>& x
);
template<class T>
valarray<T> log(
const valarray<T>& x
);
template<class T>
valarray<T> log10(
const valarray<T>& x
);
Remarks
注意
The class/parameter names in the prototype do not match the version in the header file. Some have been modified to improve readability.
Example
// explog10.cpp
// compile with: /EHsc
#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;
int main() {
// Set val_array to contain values 1, 10, 100 for the following test.
DB_VARRAY val_array(ARRAY_SIZE);
int i;
for (i = 0; i < ARRAY_SIZE; i++)
val_array[i] = pow((double)10, i);
// Display the size of val_array.
cout << "Size of val_array = " << val_array.size() << endl;
// Display the content of val_array before calling exp, log, and
// log10 functions.
cout << "val_array values:";
for (i = 0; i < ARRAY_SIZE; i++)
cout << " " << val_array[i];
cout << endl;
// rvalue_array to hold the return value from calling the exp,
// log, and log10 functions.
DB_VARRAY rvalue_array;
// ----------------------------------------------------------------
// exp() - display the content of rvalue_array
// ----------------------------------------------------------------
rvalue_array = exp(val_array);
cout << "After calling exp():";
for (i = 0; i < ARRAY_SIZE; i++)
cout << " " << rvalue_array[i];
cout << endl;
// ----------------------------------------------------------------
// log() - display the content of rvalue_array
// ----------------------------------------------------------------
rvalue_array = log(val_array);
cout << "After calling log():";
for (i = 0; i < ARRAY_SIZE; i++)
cout << " " << rvalue_array[i];
cout << endl;
// ----------------------------------------------------------------
// log10() - display the content of rvalue_array
// ----------------------------------------------------------------
rvalue_array = log10(val_array);
cout << "After calling log10():";
for (i = 0; i < ARRAY_SIZE; i++)
cout << " " << rvalue_array[i];
cout << endl;
}
Output
Size of val_array = 3
val_array values: 1 10 100
After calling exp(): 2.71828 22026.5 2.68812e+043
After calling log(): 0 2.30259 4.60517
After calling log10(): 0 1 2
Requirements
Header: <valarray>