THE STANDARD C++ CLASS LIBRARY in .NET framework

Creating QR Code JIS X 0510 in .NET framework THE STANDARD C++ CLASS LIBRARY

Table 37-4

Transcendental Functions Defined for valarray (continued)

// Demonstrate valarray #include <iostream> #include <valarray> #include <cmath> using namespace std; int main() { valarray<int> v(10); int i; for(i=0; i<10; i++) v[i] = i; cout << "Original contents: "; for(i=0; i<10; i++) cout << v[i] << " "; cout << endl; v = vcshift(3); cout << "Shifted contents: "; for(i=0; i<10; i++) cout << v[i] << " "; cout << endl; valarray<bool> vb = v < 5; cout << "Those elements less than 5: "; for(i=0; i<10; i++) cout << vb[i] << " "; cout << endl << endl; valarray<double> fv(5); for(i=0; i<5; i++) fv[i] = (double) i; cout << "Original contents: "; for(i=0; i<5; i++) cout << fv[i] << " "; cout << endl;

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fv = sqrt(fv); cout << "Square roots: "; for(i=0; i<5; i++) cout << fv[i] << " "; cout << endl; fv = fv + fv; cout << "Double the square roots: "; for(i=0; i<5; i++) cout << fv[i] << " "; cout << endl; fv = fv - 100; cout << "After subtracting 10 from each element:\n"; for(i=0; i<5; i++) cout << fv[i] << " "; cout << endl; return 0; }

Its output is shown here:

Original contents: 0 1 2 3 4 5 6 7 8 9 Shifted contents: 3 4 5 6 7 8 9 0 1 2 Those elements less than 5: 1 1 0 0 0 0 0 1 1 1 Original contents: 0 1 2 3 4 Square roots: 0 1 141421 173205 2 Double the square roots: 0 2 282843 34641 4 After subtracting 10 from each element: -10 -8 -717157 -65359 -6

The <valarray> header defines two utility classes called slice and gslice These classes encapsulate a slice (ie, a portion) from an array These classes are used with the subset forms of valarray's operator[ ]

The slice class is shown here:

class slice { public: slice(); slice(size_t start, size_t len, size_t interval); size_t start() const; size_t size() const; size_t stride(); };

The first constructor creates an empty slice The second constructor creates a slice that specifies the starting element, the number of elements, and the interval between elements (that is, the stride) The member functions return these values Here is a program that demonstrates slice

// Demonstrate slice #include <iostream> #include <valarray> using namespace std; int main() { valarray<int> v(10), result; unsigned int i; for(i=0; i<10; i++) v[i] = i; cout << "Contents of v: "; for(i=0; i<10; i++) cout << v[i] << " "; cout << endl; result = v[slice(0,5,2)]; cout << "Contents of result: "; for(i=0; i<resultsize(); i++) cout << result[i] << " "; return 0; }

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The output from the program is shown here:

Contents of v: 0 1 2 3 4 5 6 7 8 9 Contents of result: 0 2 4 6 8

As you can see, the resulting array consists of 5 elements of v, beginning at 0, that are 2 apart The gslice class is shown here:

class gslice { public: gslice(); gslice()(size_t start, const valarray<size_t> &lens, const valarray<size_t> &intervals); size_t start() const; valarray<size_t> size() const; valarray<size_t> stride() const; };

The first constructor creates an empty slice The second constructor creates a slice that specifies the starting element, an array that specifies the number of elements, and an array that specifies the intervals between elements (that is, the strides) The number of lengths and intervals must be the same The member functions return these parameters This class is used to create multidimensional arrays from a valarray (which is always one-dimensional) The following program demonstrates gslice

// Demonstrate gslice() #include <iostream> #include <valarray> using namespace std; int main() { valarray<int> v(12), result; valarray<size_t> len(2), interval(2); unsigned int i; for(i=0; i<12; i++) v[i] = i; len[0] = 3; len[1] = 3;