isVowel

#include <iostream>

using namespace std;

int main(int argc, char const* argv[])
{
    char ch;
    while (true) {
        cout << "Give me a letter: ";
        cin >> ch;

        if (ch >= 'A' && ch <= 'Z') {
            ch += 'a' - 'A';
        } else if (!(ch >= 'a' && ch <= 'z')) {
            cout << ch << " isn't a letter" << endl;
            continue;
        }

        switch (ch) {
        case 'a':
        case 'e':
        case 'i':
        case 'o':
        case 'u':
            cout << "It's a vowel letter." << endl;
            break;

        default:
            cout << "It isn't a vowel letter" << endl;
            break;
        }
    }
    return 0;
}