Receiving a string, checking for a Capital Letter - c++

Question

What Im trying to do is check if the user-supplied string has a capital letter or not.
The first part of the code with the enumerated constant, is just there for another method,
which I got to work using numbers assigned to the words Sunday = 7, Monday=1, Tuesday=2, etc. I'm trying have the user not supply numbers, but the actual word (Sunday, Monday, Tuesday), but I want them to specify the day of the week with a capital letter.
Problem I get: compiles fine, but anything you type in is somehow redirected along an execution path that always returns "Retype w/ a capital letter." This happens if I type in fjdkalfda or sunday or Sunday or whatever. Here is the code. Sorry if its not in code format, first time user of Stack Overflow.
#include <iostream>
#include <string>
#include <cstring>
using namespace std;
int main(){
/*enum DaysOfWeek {
Monday = 1,
Tuesday,
Wednesday,
Thursday,
Friday,
Saturday,
Sunday
};*/ //I'm not using this, but I can get my code to work with this
//enumerated constant by asking the user to input a number corresponding
//to the day of the week and then using if-else statements to check, say,
// int Day;
// cin >> Day
// then use if statements to check if Day = a certain number, to give output
cout << "Enter the day of week with a capital letter: ";
string Day;
getline(cin, Day);
if (Day == ("monday") || ("tuesday"))
cout << "Retype w/ a capital letter" << endl;
else if (Day == ("wednesday") || ("thursday"))
cout << "Retype w/ a capital letter" << endl;
else if (Day == ("friday") || ("saturday"))
cout << "Retype w/ a capital letter" << endl;
else if (Day == ("sunday"))
cout << "Retype w/ a capital letter" << endl;
else
{
if (Day == "Monday")
cout << "Moon" << endl;
else if (Day == "Tuesday")
cout << "Mars" << endl; //continue with the days etc...
}
return 0;
}

Answer 1

One would observe that there is a function called toupper which can turn a lower case letter into upper case, and leave an upper case letter alone. Perhaps you can reuse this function to help solve your problem with less code.
I am inferring from your code that you are only interested in verifying that the first letter is a capital letter. Is that correct?

Answer 2

There is an isupper function in ctype.h that returns true if a char is upper case:
#include <ctype.h>
...
isCapitalized = isupper(str[0]);
...

Answer 3

I'm assuming you're actually not bothered about capitol letters if we can somehow organize the input choice in an enum type. Instead of this enum classes would be a better choice if you have C++11. If not, it would be quite easy to change this code for normal enums
If you're using gcc/g++, you may need to include prefix -std=c++11
Note: you may want to add another enum element to enum class Days such as null_day. Or even better, Make sure user inputs the correct day, until he/she does, don't carry on with program (hint: use while loop when using getline)
#include <iostream>
#include <string>
#include <cstring>
#include <algorithm>
using std::string;
using std::transform;
using std::cout;
using std::cin;
using std::endl;
// only in C++ 11
enum class Day {Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday};
int main () {
cout << "Enter the day of week: ";
// store day from user input, transform all to lower case so
// we don't bother with user input type (only error in spelling will be the problem now)
string get_day;
getline(cin, get_day);
transform(get_day.begin(), get_day.end(), get_day.begin(), tolower);
// define instance of enum class Day, and sort out what day user has input
// note that if you do not initialize myDay object, it will set to the first
// element in the enum class Day above (which is Monday). This will happen
// if user input is not allowed to initialize it. See the << >> section below
Day myDay;
if (get_day == "monday")
myDay = Day::Monday;
else if (get_day == "tuesday")
myDay = Day::Tuesday;
else if (get_day == "wednesday")
myDay = Day::Wednesday;
else if (get_day == "thursday")
myDay = Day::Thursday;
else if (get_day == "friday")
myDay = Day::Friday;
else if (get_day == "saturday")
myDay = Day::Saturday;
else if (get_day == "sunday")
myDay = Day::Sunday;
else
<< ERROR CODE HERE >>
<< MAYBE A WHILE LOOP UNTIL USER INPUTS CORRECT DATA >>
// perform your calculations/operations/etc separate from above
if (myDay == Day::Monday)
cout << "Moon" << endl;
else if (myDay == Day::Tuesday)
cout << "Mars" << endl; //continue with the days etc...
return 0;
}