int main(void) {
    string userInput;
 
    cout << "Enter a string to be converted:" << endl;
    cin >> userInput;
    for (int index = 0; index <= userInput.length(); index++) {
        cout << userInput[index] << endl;
        }
 
 
    system("pause");
    return 0;
}

input: hello dolly
output: hello

#define MAX_LENGTH 256
int main(void) {
    char userInput[MAX_LENGTH]; // use a character array not string
 
    cout << "Enter a string to be converted:" << endl;
    cin.get(userInput,256); // cin.get(char*,int) not cin >> ;
    cin.ignore(); // ignore the leading '\n' character
    for (int index = 0; index < strlen(userInput) /* strlen gives you the length of a character array */; index++) {
        cout << userInput[index] << endl;
        }
    system("pause");
    return 0;
}