As for finding the largest you need to see how many if-then/if-else statements you need, if you need, now you can either write them seperate like you have or a different way.
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if (a > b && a > c && a > d && a > e)
largest = a;
cout << "The largest number is << a << endl;
else if (b > a && b > c && b > d && b > e)
largest = b;
cout << "The largest number is << b << endl;
and so on
your making more work for you because your doing it sepeately, meaning youll have more if-then statements.
cout is whats use to print something to the screen and cin allows the program to get the user input from the keyboard.