Why is my second cin bound with the first cin? The output is below(C++)

Question

This program is supposed to show the position of an alphabet input by the user and then ask the user to input a sentence and make everything in that sentence uppercase. I assumed it to be very easy but I face this problem where my second cin don't show and it just bounds onto the first cin. Please help, thanks. Input with just one characterInput with multiple characters

#include <iostream>
#include <cctype>
using namespace std;

void position_alphabet();
void convert_case();

int main()
{
    char characters[50];
    position_alphabet();
    convert_case();
    return 0;
}

void position_alphabet()
{
    char alphabet;
    char lowered_alphabet;
    cout << "Enter an alphabet: ";
    cin >> alphabet;
    if (isalpha(alphabet))
    {
        if (isupper(alphabet))
        {
            lowered_alphabet = tolower(alphabet);
            cout << "Position of the alphabet: " << lowered_alphabet - 96 << endl;
        }
        else
        {
            cout << "Position of the alphabet: " << int(alphabet) - 96 << endl;
        }
    }
    else
    {
        cout << "Error! Please enter an alphabet" << endl;
    }
    return;
}

void convert_case()
{
    char characters[50];
    cout << "Enter a sentence: ";
    cin.get(characters, 50);
    cout << "Everything to upper: ";
    int len = strlen(characters);
    for (int i = 0; i < len; i++)
    {
        if (islower(characters[i]))
        {
            characters[i] = toupper(characters[i]);
        }
        cout << characters[i];
    }
    return;
}