(Financial: credit card number validation) Credit card numbers follow certain pat- terns. A credit card number must have between 13 and 16 digits. It must start with: 4 for Visa cards 5 for Master cards 37 for American Express cards 6 for Discover cards In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The algorithm is useful to determine whether a card number is entered correctly or whether a credit card is scanned correctly by a scanner. Credit card numbers are generated following this validity check, commonly known as the Luhn check or the Mod 10 check, which can be described as follows (for illustra- tion, consider the card number 4388576018402626): 1. Double every second digit from right to left. If doubling of a digit results in a two-digit number, add up the two digits to get a single-digit number. 4388576018402626 → 2 * 2 = 4 → 2 * 2 = 4 → 4 * 2 = 8 → 1 * 2 = 2 6 * 2 = 12 (1+ 2 = 3) → 5 * 2 = 10 (1+ 0 = 1) → 8 * 2 = 16 (1 + 6 = 7) → 4 * 2 = 8

(Factorials) Factorials are used frequently in probability problems. The factorial of a positive integer n (written n! and pronounced “n factorial”) is equal to the product of the positive integers from 1 to n. Write an application that calculates the factorials of 1 through 20. Use type long . Display the results in tabular format. What difficulty might prevent you from calculating the factorial of 100?

(IN C LANGUAGE) Binary-Decimal / Decimal Binary . Between 0 and 255 a number will be decided randomly by computer. Then asks to user 3 times a random digit of binary value of the that number. If user enters wrong number for a digit program will select another random number and ask random times random digit. For example: Computer selected number as 163 ( Which is 10100011) What is the digit 2 (question 1/3) :User enter 1 CorrectWhat is the digit 4 (question 2/3) : User enter 0 CorrectWhat is the digit 7 (question 3/3) : User enter 0 CorrectUser finished the quest with 3 input .