Case Study: Lottery in C++

The lottery program involves generating random numbers, comparing digits, and using Boolean operators.

Suppose you are to develop a program to play the lottery. The program randomly generates a lottery of a two-digit number, prompts the user to enter a two-digit number, and determines whether the user wins according to the following rule:

1. If the user input matches the lottery number in the exact order, the award is $10,000.
2. If all the digits in the user input match all the digits in the lottery number, the award is $3,000.
3. If one digit in the user input matches a digit in the lottery number, the award is $1,000.

Note that the digits of a two-digit number may be 0. If a number is less than 10, we assume the number is preceded by a 0 to form a two-digit number. For example, number 8 is treated as 08 and number 0 is treated as 00 in the program. Listing 3.7 gives the complete program.

LisTing 3.7 Lottery.cpp

1 #include <iostream>

2 #include <ctime> // for time function

3 #include <cstdlib> // for rand and srand functions

4 using namespace std;

5

6 int main()

7 {

8    // Generate a lottery

9     srand(time(0));

10    int lottery = rand() % 100;

11 

12    // Prompt the user to enter a guess

13    cout << “Enter your lottery pick (two digits): “;

14    int guess;

15    cin >> guess;

16

17    // Get digits from lottery

18    int lotteryDigit1 = lottery / 10;

19    int lotteryDigit2 = lottery % 10;

20

21    // Get digits from guess

22    int guessDigit1 = guess / 10;

23    int guessDigit2 = guess % 10;

24

25    cout << “The lottery number is ” << lottery << endl;

26

27    // Check the guess

28    if (guess == lottery)

29    cout << “Exact match: you win $10,000” << endl;

30    else if (guessDigit2 == lotteryDigit1

31    && guessDigit1 == lotteryDigit2)

32    cout << “Match all digits: you win $3,000” << endl;

33    else if (guessDigit1 == lotteryDigit1

34       || guessDigit1 == lotteryDigit2

35       || guessDigit2 == lotteryDigit1

36       || guessDigit2 == lotteryDigit2)

37      cout << “Match one digit: you win $1,000” << endl;

38    else

39      cout << “Sorry, no match” << endl;

40

41    return 0;

42 }

The program generates a lottery using the rand() function (line 10) and prompts the user to enter a guess (line 15). Note that guess % 10 obtains the last digit from guess, and guess / 10 obtains the first digit from guess, since guess is a two-digit number (lines 22-23).

The program checks the guess against the lottery number in this order:

1. First, check whether the guess matches the lottery exactly (line 28).
2. If not, check whether the reversal of the guess matches the lottery (lines 30-31).
3. If not, check whether one digit is in the lottery (lines 33-36).
4. If not, nothing matches and display “Sorry, no match” (lines 38-39).

Source: Liang Y. Daniel (2013), Introduction to programming with C++, Pearson; 3rd edition.