Tutorial 12 Craps Game Application: Introducing Random Number Generation and Enumerations

Transcription

1 Tutorial 12 Craps Game Application: Introducing Random Number Generation and Enumerations Outline 12.1 Test-Driving the Craps Game Application 12.2 Random Number Generation 12.3 Using an enum in the Craps Game Application 12.4 Using Random Numbers in the Craps Game Application 12.5 Wrap-Up

2 Objectives In this tutorial, you will learn to: Use simulation techniques that employ random-number generation. Use the rand math library function to generate random numbers. Use enumerations to enhance code readability.

3 12.1 Test Driving the Craps Game Application

4 12.1 Test Driving the Craps Game Application (Cont.) Figure 12.1 Example of an initial appearance of Craps Game application. Figure 12.2 Player winning on the first roll by rolling an 11.

5 12.1 Test Driving the Craps Game Application (Cont.) Figure 12.3 Player losing on the first roll by rolling a 3. Figure 12.6 Player losing by rolling a 7 before matching the point value.

6 12.1 Test Driving the Craps Game Application (Cont.) Figure 12.5 Player winning the game by matching the point value before rolling a 7. Figure 12.6 Player losing by rolling a 7 before matching the point value.

7 <cstdlib> c standard utility library header file cstdlib is part of the C++ Standard Library. The C++ Standard Library includes 18 header files from the C Standard Library. The cstdlib include/header file contains the function declarations for commonly used library functions which either don't fit somewhere else, or, cannot be declared in the normal place for other reasons. cstdlib includes several general purpose functions, including dynamic memory management, random number generation, communication with the environment, integer arithmetic, searching, sorting and converting. Function prototypes declared in cstdlib are defined within the std namespace.

8 <cstdlib> c standard utility library header file (Cont.) Each C++ header file has the same name as the C language version but with a "c" prefix and no extension. In this case, the C++ equivalent for the C language header file <stdlib.h> is <cstdlib>. If you look inside the cstlib file you will find the following preprocessor directive. #include <stdlib.h>

9 <cstdlib> c standard utility library header file (Cont.) Figure 12.9 Including the <cstdlib> and <ctime> standard library header files so that the application can produce random numbers. Including the <ctime> standard library header file Including the <cstdlib> standard library header file

10 Random Number Generation rand function : Generates a pseudorandom number between 0 and RAND_MAX RAND_MAX is defined in stdlib.h as /* Maximum value that can be returned by the rand function. */ #define RAND_MAX 0x7fff #define directive substitutes token-string for all subsequent occurrences of an identifier in the source file. 0x7fff = 32,767 10

11 Random Number Generation Seed the rand function with srand The value used to seed rand determines the sequence of pseudorandom numbers it generates Use srand(time(0)) to make rand generate a different sequence of pseudorandom numbers each time the application runs time returns the current calendar time in seconds since 1/1/ :00:00. The function prototype for time is in the <ctime> C++ Standard Library header file Figure Using the time and srand functions to seed the rand function. Seeding the rand function

12 Random Number Generation (Cont.) Exp ression Resulting ra nge rand() 0 to RAND_MAX [0 to at least 32,767] rand() % 30 0 to rand() % to 19 Figure 12.7 rand func tion c a ll exp ressions with ranges of rand om numb ers p roduc ed. Using the modulus operator to generate random numbers within a certain range

13 Random Number Generation rolldice Example Figure Declaring the rolldice function prototype. Declaring the rolldice function prototype rolldice function simulates rolling two dice Returns the value of the sum of the two dice

14 Random Number Generation rolldice Example Figure Defining the rolldice function. Defining local variables to store die values Getting two random numbers and storing their sum

15 Using the rolldice function Random Number Generation rolldice Example rolls two dice, displays their values and returns their sum Figure Rolling the dice. Rolling the dice

16 Using an enum in the Craps Game Application In C and C++, enum types can be used to set up collections of user-defined (or programmer-defined) named integer constants. (The keyword enum is short for ''enumerated''.) Figure Using the enum keyword to declare an enumeration. Declaring an enumeration In this example, user-defined type Status can only be one of three values CONTINUE, WON or LOST

17 Using an enum in the Craps Game Application (Cont.) Enumeration constants start at 0, unless specified otherwise, and increment by 1 enum FooSize {SMALL=10, MEDIUM=100, LARGE=1000}; Attempting to assign another value to an enumeration constant after it has been defined is an error.

18 Using an enum in the Craps Game Application (Cont.) Figure Defining a variable to store values declared in the Status enumeration. Defining a variable of type Status

19 Using an enum in the Craps Game Application (Cont.) Assigning an enumeration constant to a variable of the enumeration type. Figure default case in main. User must match the point Displaying the point A common syntax error is to assign the integer equivalent of an enumeration constant to a variable of the enumeration type.

20 Using an enum in the Craps Game Application (Cont.) Figure 12.8 Pseudocode for the Craps Game application. Roll the two dice using random numbers Calculate and display the sum of the two dice Switch based on the sum of the two dice: Case where the sum is 7 or 11 Display the winning message Case where the sum is 2, 3 or 12 Display the losing message Default case Set the value of the point to the sum of the dice and display the value While the player has not won or lost Roll the two dice using random numbers Calculate and display the sum of the two dice If the player rolled the point Display the winning message If the player rolls a 7 Display the losing message

21 Using an enum in the Craps Game Application (Cont.) Figure Defining constants in the Craps Game application. Defining constants

22 Using an enum in the Craps Game Application (Cont.) Figure switch statement in main. Winning on the first roll Losing on the first roll

23 1 // Tutorial 12: CrapsGame.cpp 2 // This application plays a simple craps game. 3 #include <iostream> // required to perform C++ stream I/O 4 #include <string> // required to access string functions 5 #include <ctime> // contains prototype for function time 6 7 // contains function prototypes for srand and rand 8 #include <cstdlib> 9 10 using namespace std; // for accessing C++ Standard Library members int rolldice( void ); // function prototype 13 Include the <ctime> standard library header file CrapsGame.cpp (1 of 6) Include the <sdtdlib> standard library header file Declare the rolldice function prototype

24 14 // function main begins program execution 15 int main() 16 { 17 // constants representing winning dice rolls 18 const int LUCKY_SEVEN = 7; 19 const int YO_LEVEN = 11; // constants representing losing dice rolls 22 const int SNAKE_EYES = 2; 23 const int TREY = 3; 24 const int BOX_CARS = 12; 25 const int CRAPS = 7; // loses only after first roll // enumeration constants represent game status 28 enum Status { CONTINUE, WON, LOST }; int sum; // stores sum of the dice 31 int mypoint; // stores the player's point 32 string input; // stores input after each dice roll Status gamestatus; // can contain CONTINUE, WON or LOST 35 CrapsGame.cpp (2 of 6) Define constants Declare an enumeration Define a variable of the Status type

25 36 // randomize random number generator using current time 37 srand( time( 0 ) ); sum = rolldice(); // first roll of the dice // determine game status and point based on sum of dice 42 switch ( sum ) 43 { 44 // win on first roll 45 case LUCKY_SEVEN: 46 case YO_LEVEN: 47 gamestatus = WON; 48 break; // lose on first roll 51 case SNAKE_EYES: 52 case TREY: 53 case BOX_CARS: 54 gamestatus = LOST; 55 break; 56 Seed the rand function Win on the first roll Lose on the first roll Roll the dice CrapsGame.cpp (3 of 6)

26 57 // remember point 58 default: 59 gamestatus = CONTINUE; 60 mypoint = sum; 61 cout << "Point is " << mypoint << endl; 62 break; // optional } // end switch // repeat while the game is not complete 67 while ( gamestatus == CONTINUE ) 68 { 69 cout << "\npress enter to continue..."; 70 getline( cin, input ); // pauses until user presses Enter sum = rolldice(); // roll dice again // determine game status 75 if ( sum == mypoint ) // win by matching point 76 { 77 gamestatus = WON; 78 } // end if User must match the point Repeat until user has won or lost Roll the dice again Determine if user won CrapsGame.cpp (4 of 6)

27 79 else if ( sum == CRAPS ) // lose by rolling 7 80 { 81 gamestatus = LOST; 82 } // end else if } // end while // display won or lost message 87 if ( gamestatus == WON ) 88 { Determine if user lost 89 cout << "Player wins" << endl << endl; 90 } // end if 91 else 92 { 93 cout << "Player loses" << endl << endl; 94 } // end else if return 0; // indicates successful termination } // end function main 99 Display game outcome CrapsGame.cpp (5 of 6)

28 100 // roll dice, calculate sum and display results 101 int rolldice( void ) 102 { 103 int die1; // stores the value of the first die 104 int die2; // stores the value of the second die 105 int dicesum; // stores the sum of the dice values die1 = 1 + rand() % 6; // pick random die1 value 108 die2 = 1 + rand() % 6; // pick random die2 value 109 dicesum = die1 + die2; // sum die1 and die // display results of this roll 112 cout << "\nplayer rolled " << die1 << " + " << die2 113 << " = " << dicesum << endl return dicesum; // return the sum of dice } // end function rolldice CrapsGame.cpp (6 of 6) Generate random numbers and calculate their sum Display the die values and their sum