Bulls and Cows

This App generate secret number which the user will try to guess. The user will first make a blind guess by keying in the four digits. The app will then respond with a clue.
If any digit from the guessed number is correctly located in the secret number, the app will give you a Bull. If the digit is contained in secret number but in incorrect place , you will get a Cow.
Example:

Secret number: 4271
You Guess: 1234
App Responds with : 1 bull and 2 cows. (The bull is "2", the cows are "4" and "1".)

Thus you can keep guessing using the clues till you get 4 bulls

You will be allowed 10 attempts.