[学习笔记]C++17学习第7天

mdl2999_52pj

# include <iostream>
# include <cctype>
// c++17
using namespace std;

int main()
{
    char letter{};
    cout << "Enter a letter: ";
    cin >> letter;
    int count{0};

    if (isalpha(letter))
    {
        switch(auto lower{static_cast<char>(tolower(letter))}; lower)
        {
            case 'a':
            case 'e':
            case 'i':
            case 'o':
            case 'u':
                cout << "You entered a vowel.\n";
                [[fallthrough]];
            default:
                count ++;
                break;

        }
    }
    else
    {
        cout << "You didn't enter a letter.\n";
    }
    cout << "You entered " << count << " char(s)." << endl;
}

mdl2999_52pj

# include <iostream>
// c++17
using namespace std;

int main()
{
    double rainfall[] {1.1, 2.8, 3.4, 3.7, 2.1, 2.3, 1.8, 0.0, 0.3, 0.9, 0.7, 0.5};
    double copy[sizeof(rainfall)/sizeof(rainfall[0])]{};
    for (size_t i{}; i!= sizeof(rainfall)/sizeof(rainfall[0]); ++i)
        copy[i] = rainfall[i];

    for (size_t i{}; i!= sizeof(copy)/sizeof(copy[0]); ++i)
        cout << copy[i] << ", ";
    cout << endl;
}

mdl2999_52pj

# include <iostream>
# include <array>
// c++17
using namespace std;

int main()
{
    int values[] {2,3,5,7,11,13,17,19,23,29};
    for(size_t i{}; i!= size(values); ++i)
        cout << values[i] << ',';
    cout << endl;
}

mdl2999_52pj

# include <iostream>
# include <iomanip>
# include <array>
// c++ 17
using namespace std;

int main()
{
    constexpr double pi {3.14159265358979323846};
    constexpr int perline{3};
    int line_count {};

    for (double radius{0.2}; radius < 10.0; radius += .2)
    {
        cout << fixed << setprecision(2) << "radisu=" <<  setw(6) << radius << ", area=" << setw(8)<< pi*radius*radius;
        if (++line_count%perline==0)
        {
            cout << endl;
        }
        else
        {
            cout << '\t';
        }

    }
}

DayBreak

坚持就是胜利，还有c++20标准