My First Command-Line Program

Transcription

1 1. Tutorial Overview My First Command-Line Program In this tutorial, you re going to create a very simple command-line application that runs in a window. Unlike a graphical user interface application where you click on objects, a commandline application requires you to type in commands and the outputs are usually printed as text. To do this tutorial, you need to have the following tools: An Intel-based Mac running Leopard (OS X or later). The iphone SDK. You can download the free version from the Apple web site. The SDK includes all of the necessary software tools that you will need to develop the apps. However, the free version will only allow you to run your app in the iphone simulator running on your development machine. In order to run your app on the iphone or ipod Touch, you will have to get the paid version which costs $99 for the standard version. Page 1 of 9 Copyright Enoch Hwang 2009

2 2. Creating Your Project The main tool you use to create applications for the iphone is Xcode-Apple s IDE (integrated development environment). Launch Xcode. By default it s in /Developer/iPhone Applications. If the welcome window comes up, you can just close it. Create a new project by choosing from the menu File > New Project. The notation used here means that you first click on the File menu and then you click on New Project. You should see a window for choosing a template for your new project like this. Select this template In the left side of the window, make sure that Application under the OS X section is selected. If not, then just click on it to select it. Select the Command Line Tool template icon, and click Next. Page 2 of 9 Copyright Enoch Hwang 2009

3 A New Project window appears to allow you to specify the name of your new project. Type in MyFirstLineProgram as the Product Name, and select C++ for the Type. Click Next to go to the next screen. Enter the product (project) name Select the C++ type Select a suitable location to save your project such as the Desktop, and then click the Create button to create the project. Page 3 of 9 Copyright Enoch Hwang 2009

4 You should now see the main project window with the name MyFirstLineProgram containing all of the necessary files for your project like this. Run button to run your program Your main program always called main.cpp Your program inside the main.cpp file Console output from running your program This window consists of three sections. The left section shows the files in your project. The main file that you will be using to write your code is always called main.cpp. The top-right section shows the content of the file that you have selected in the left section. You can change the size of each section by dragging the horizontal or vertical separator border. Since Xcode has included everything that you need to run the program inside your newly created project, you can now run the program by clicking on the triangle Run button in the toolbar. The result from running your program is shown in the console area at the bottom-right section of the window. In the example, the words Hello, World! are printed out. Page 4 of 9 Copyright Enoch Hwang 2009

5 3. The Template Program To see the sample C++ program that you just ran, select the program file main.cpp in the left section of your project window. The content of the program is listed in the top-right of the window. For clarity, the main.cpp program code is listed again below. // // main.cpp // MyFirstLineProgram // // Created by Enoch Hwang on 1/16/14. // Copyright (c) 2014 cptg121. All rights reserved. // #include <iostream> using namespace std; int main(int argc, const char * argv[]) { } // insert code here... cout << "Hello, World!\n"; return 0; Probably the first thing that stands out in the program is the multi-color words. Xcode uses these colors to help you to identify the different features of the code. For example, words in purple such as int, return, and cout are keywords; words in black such as main are user-identifier names that you create; and words in green are comments. You will learn more about keywords, user-identifiers that you create and other features of the code very soon. Another thing that you might notice is that not all of the lines line up at the left margin, and they don t go all the way to the right margin. Furthermore, there are some empty lines. C++ doesn t care about empty lines and spaces. You can start typing your statements anywhere. However, it is much easier to read your program if you separate different sections of code with empty lines, and indent lines that are inside the same block. This is a good programming habit to get into. A final note is that C++ treats uppercase and lowercase letters as different characters. So, for example, don t type Cout for the word cout, otherwise you will get an error message when you try to run the program. Let us now look at the program in more detail. Notice that the program that I have is slightly different from the template program that you have. Modify your program to match my program. The first and second lines in the program #include <iostream> using namespace std; Page 5 of 9 Copyright Enoch Hwang 2009

6 tells the compiler (or computer, for beginners) to insert the system file iostream into your program just as if you had typed the file in yourself at that point. The system file iostream contains input and output functions that you will need to use in your program. Instead of having to reinvent the wheel and retype everything manually, you just insert it in using the #include statement. For Objective-C, it will be #import instead of #include. The using line tells the computer to use the name std. The next line in the program int main (int argc, const char * argv[]) { specifies that the name of the program is main. main is a special name used to indicate that the program begins its execution here. The two parameters or arguments, argc and argv[ ], inside the parenthesis are for passing data into main. We won t be using them so you can either just leave them there or remove them. The int keyword in front of main specifies that when main terminates execution, it will return an integer value. The statements or commands that the main program executes are enclosed between the opening brace { on the next line and the closing brace } at the very end of the program listing. For now, all statements that you write for your program must be between these two braces. The line starting with the two slashes // // insert code here... is a comment line. Comments are only for documentation purposes, i.e., to tell the programmer what the code is doing, and are ignored by the compiler (computer). Again, it is a good habit to write good comments for your programs. The first statement in the program cout << "Hello, World!" << endl; prints out the string Hello, World! without the double quotes, on the console. The command here is cout and the string to be printed out is enclosed inside the two double quotes. If you want the program to print something else instead of the words Hello, World!, then you will replace the string inside the double quotes with whatever you want to print. The endl tells the computer to do a carriage return, i.e. start a new line. In the original template, the cout line had std::cout instead. This is needed if you had not typed in the using namespace std line earlier. Having the using namespace std line allows you to just type cout. Page 6 of 9 Copyright Enoch Hwang 2009

7 The last statement return 0; tells the computer that the execution of the program is to terminate here and to return a value, in this case, a 0. Recall the int keyword in front of the main statement specifies the type of value the program will return when it terminates. The convention is that a 0 means that the program terminated normally. For beginners, all of the statements in this template program except for the cout statement need to be exactly the same. The comment, of course, can be modified or deleted because the compiler doesn t care about it. In addition to the cout command there is another command for printing things out. This is the printf command. Instead of the cout statement in the template, you can replace it with printf("hello, World!"); To start a new line with the printf command, you need to print the two characters \n inside the double quote like this printf("hello, World!\n"); Page 7 of 9 Copyright Enoch Hwang 2009

8 4. Exercises 1. Modify the Hello World program so that it prints out your name instead of the word World for example, Hello Amy! 2. Write a program to print your name ten times on one line using the cout command. 3. Write a program to print your name ten times on ten separate lines using ten cout commands. 4. Write a program to print your name ten times on ten separate lines using only one cout command. 5. Write a program to print your name ten times on ten separate lines using ten printf commands. 6. Write a program to print your name ten times on ten separate lines using only one printf command. 7. Write a program to print the numbers from 0 to 9 on one line. 8. Write a program to print the numbers from 0 to 9 on ten different lines. 9. Write a program to print the following picture using asterisks: 10. Write a program to print the following picture asterisks: * * * * * * 11. Write a program to print the following picture asterisks: * *** ***** ******* ********* Page 8 of 9 Copyright Enoch Hwang 2009

9 12. Write a program to print an address label with three lines, your name on the first line, your street address on the second line, and the city, state and zip on the third line. 13. Write a program to print the sender and receiver address that is formatted like on an envelope. Three lines for the sender address at the top left corner and three lines for the receiver address in the middle. 14. Write a program to print out the multiplication table from 1 to 10 similar to this: You need to line up the numbers nicely, i.e. they are right-aligned with all the unit digits lined up. Is it easier to use just one cout command or several cout commands to do this question? 15. Write a program to print out the famous quote, Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal. You need to also print out the two double-quotes. Hint: Use the escape character \ to print out the double-quote. 16. Write a program to print out the following picture using the symbols /, \,, _, and O. Hint: Use the escape character \ to print out the back-slash character \. \_O_ \ / \ Page 9 of 9 Copyright Enoch Hwang 2009