PracticeDev/study_cpp/cpp_primer_source_code/Chapter 16/vslice.cpp

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2022-12-20 17:31:11 +08:00
// vslice.cpp -- using valarray slices
#include <iostream>
#include <valarray>
#include <cstdlib>
const int SIZE = 12;
typedef std::valarray<int> vint; // simplify declarations
void show(const vint & v, int cols);
int main()
{
using std::slice; // from <valarray>
using std::cout;
vint valint(SIZE); // think of as 4 rows of 3
int i;
for (i = 0; i < SIZE; ++i)
valint[i] = std::rand() % 10;
cout << "Original array:\n";
show(valint, 3); // show in 3 columns
vint vcol(valint[slice(1,4,3)]); // extract 2nd column
cout << "Second column:\n";
show(vcol, 1); // show in 1 column
vint vrow(valint[slice(3,3,1)]); // extract 2nd row
cout << "Second row:\n";
show(vrow, 3);
valint[slice(2,4,3)] = 10; // assign to 2nd column
cout << "Set last column to 10:\n";
show(valint, 3);
cout << "Set first column to sum of next two:\n";
// + not defined for slices, so convert to valarray<int>
valint[slice(0,4,3)] = vint(valint[slice(1,4,3)])
+ vint(valint[slice(2,4,3)]);
show(valint, 3);
// std::cin.get();
return 0;
}
void show(const vint & v, int cols)
{
using std::cout;
using std::endl;
int lim = v.size();
for (int i = 0; i < lim; ++i)
{
cout.width(3);
cout << v[i];
if (i % cols == cols - 1)
cout << endl;
else
cout << ' ';
}
if (lim % cols != 0)
cout << endl;
}