1.7. Test-Driving a C++ Application

1.7. Test-Driving a C++ Application In this section, you'll run and interact with your first C++ application. You'll begin by running an entertaining guess-the-number game, which picks a number from 1 to 1000 and prompts you to guess it. If your guess is correct, the game ends. If your guess is not correct, the application indicates whether your guess is higher or lower than the correct number. There is no limit on the number of guesses you can make. [Note: This application uses the same correct answer every time the program executes (though this may vary by compiler), so you can use the same guesses we use in this section and see the same results as we walk you through interacting with your first C++ application.] We'll demonstrate running a C++ application in two ways—using the Windows XP Command Prompt and using a shell on Linux (similar to a Windows Command Prompt). The application runs similarly on both platforms. Many development environments are available in which readers can compile, build and run C++ applications, such as Eclipse, GNU C++, Microsoft Visual C++, etc. In the following steps, you'll run the application and enter various numbers to guess the correct number. Throughout the book, we use fonts to distinguish between features you see on the screen (e.g., the Command Prompt) and elements that are not directly related to the screen. Our convention is to emphasize screen features like titles and menus (e.g., the File menu) in a semibold sans-serif Helvetica font and to emphasize filenames, text displayed by an application and values you should enter into an application (e.g., GuessNumber or 500) in a sans-serif Lucida font. As you have noticed, the defining occurrence of each key term is set in bold italic. For the figures in this section, we highlight the user input required by each step and point out significant parts of the application. To make these features more visible, we have modified the background color of the Command Prompt window (for the Windows test drive only). To modify the Command Prompt colors on your system, open a Command Prompt, then right click the title bar and select Properties. In the "Command Prompt" Properties dialog box that appears, click the Colors tab, and select your preferred text and background colors. Running a C++ Application from the Windows XP Command Prompt Checking your setup. Read the Before You Begin section at the beginning of this book to ensure that you've copied the book's examples to your hard drive. Locating the completed application. Open a Command Prompt window. For readers using Windows 95, 98 or 2000, select Start > Programs > Accessories > Command Prompt. For Windows XP users, select Start > All Programs > Accessories > Command Prompt. To change to your completed GuessNumber application directory, type cd C:\examples\ch01\GuessNumber\Windows, then press Enter (Fig. 1.2). The command cd is used to change directories. Fig. 1.2. Opening a Command Prompt window and changing the directory. Running the GuessNumber application. Now that you are in the directory that contains the GuessNumber application, type the command GuessNumber (Fig. 1.3) and press Enter. [Note: GuessNumber.exe is the actual name of the application; however, Windows assumes the .exe extension by default.] Fig. 1.3. Running the GuessNumber application. Entering your first guess. The application displays "Please type your first guess.", then displays a question mark (?) as a prompt on the next line (Fig. 1.3). At the prompt, enter 500 (Fig. 1.4) Fig. 1.4. Entering your first guess. Entering another guess. The application displays "Too high. Try again.", meaning that the value you entered is greater than the number the application chose as the correct guess. So, you should enter a lower number for your next guess. At the prompt, enter 250 (Fig. 1.5). The application again displays "Too high. Try again.", because the value you entered is still greater than the number that the application chose as the correct guess. Fig. 1.5. Entering a second guess and receiving feedback. Entering additional guesses. Continue to play the game by entering values until you guess the correct number. The application will display "Excellent! You guessed the number!" (Fig. 1.6). Fig. 1.6. Entering additional guesses and guessing the correct number. Playing the game again or exiting the application. After you guess correctly, the application asks if you would like to play another game (Fig. 1.6). At the "Would you like to play again (y or n)?" prompt, entering the one character y causes the application to choose a new number and displays the message "Please type your first guess." followed by a question mark prompt (Fig. 1.7) so you can make your first guess in the new game. Entering the character n ends the application and returns you to the application's directory at the Command Prompt (Fig. 1.8). Each time you execute this application from the beginning (i.e., Step 3), it will choose the same numbers for you to guess. Fig. 1.7. Playing the game again. Fig. 1.8. Exiting the game. Close the Command Prompt window. Running a C++ Application Using GNU C++ with Linux For the figures in this section, we use a bold highlight to point out the user input required by each step. The prompt in the shell on our system uses the tilde (~) character to represent the home directory, and each prompt ends with the dollar sign ($) character. The prompt will vary among Linux systems. Locating the completed application. From a Linux shell, change to the completed GuessNumber application directory (Fig. 1.9) by typing cd Examples/ch01/GuessNumber/GNU_Linux then pressing Enter. The command cd is used to change directories. Fig. 1.9. Changing to the GuessNumber application's directory after logging in to your account. ~$ cd examples/ch01/GuessNumber/GNU_Linux ~/examples/ch01/GuessNumber/GNU_Linux$ Compiling the GuessNumber application. To run an application on the GNU C++ compiler, you must first compile it by typing g++ GuessNumber.cpp -o GuessNumber as in Fig. 1.10. This command compiles the application and produces an executable file called GuessNumber. Fig. 1.10. Compiling the GuessNumber application using the g++ command. ~/examples/ch01/GuessNumber/GNU_Linux$ g++ GuessNumber.cpp -o GuessNumber ~/examples/ch01/GuessNumber/GNU_Linux$ Running the GuessNumber application. To run the executable file GuessNumber, type ./GuessNumber at the next prompt, then press Enter (Fig. 1.11). Fig. 1.11. Running the GuessNumber application. ~/examples/ch01/GuessNumber/GNU_Linux$ ./GuessNumber I have a number between 1 and 1000. Can you guess my number? Please type your first guess. ? Entering your first guess. The application displays "Please type your first guess.", then displays a question mark (?) as a prompt on the next line (Fig. 1.11). At the prompt, enter 500 (Fig. 1.12). [Note: This is the same application that we modified and test-drove for Windows, but the outputs could vary based on the compiler being used.] Fig. 1.12. Entering an initial guess. ~/examples/ch01/GuessNumber/GNU_Linux$ ./GuessNumber I have a number between 1 and 1000. Can you guess my number? Please type your first guess. ? 500 Too high. Try again. ? Entering another guess. The application displays "Too high. Try again.", meaning that the value you entered is greater than the number the application chose as the correct guess (Fig. 1.12). At the next prompt, enter 250 (Fig. 1.13). This time the application displays "Too low. Try again.", because the value you entered is less than the correct guess. Fig. 1.13. Entering a second guess and receiving feedback. ~/examples/ch01/GuessNumber/GNU_Linux$ ./GuessNumber I have a number between 1 and 1000. Can you guess my number? Please type your first guess. ? 500 Too high. Try again. ? 250 Too low. Try again. ? Entering additional guesses. Continue to play the game (Fig. 1.14) by entering values until you guess the correct number. When you guess correctly, the application displays "Excellent! You guessed the number." (Fig. 1.14). Fig. 1.14. Entering additional guesses and guessing the correct number. Too low. Try again. ? 375 Too low. Try again. ? 437 Too high. Try again. ? 406 Too high. Try again. ? 391 Too high. Try again. ? 383 Too low. Try again. ? 387 Too high. Try again. ? 385 Too high. Try again. ? 384 Excellent! You guessed the number. Would you like to play again (y or n)? Playing the game again or exiting the application. After you guess the correct number, the application asks if you would like to play another game. At the "Would you like to play again (y or n)?" prompt, entering the one character y causes the application to choose a new number and displays the message "Please type your first guess." followed by a question mark prompt (Fig. 1.15) so you can make your first guess in the new game. Entering the character n ends the application and returns you to the application's directory in the shell (Fig. 1.16). Each time you execute this application from the beginning (i.e., Step 3), it will choose the same numbers for you to guess. Fig. 1.15. Playing the game again. Excellent! You guessed the number. Would you like to play again (y or n)? y I have a number between 1 and 1000. Can you guess my number? Please type your first guess. ? Fig. 1.16. Exiting the game. Excellent! You guessed the number. Would you like to play again (y or n)? n ~/examples/ch01/GuessNumber/GNU_Linux$