Introduction to C++

C++ is one of many programming languages. When you install a Desktop IDE (Interactive Development Environment) like Microsoft Visual Studio or XCode, it usually comes with many other programming languages. For example you might see options to write Swift, C#, Java or Objective-C programs. Replit, like these others, offers a wide array of options. We will, however, focus on developing console mode C++ code throughout these labs. It can be confusing to know which options to pick at first. In this lab we want you to know how to set up a simple C++ program of the right type and run it.

Creating Your First C++ Program

For your first C++ program, you will build a console mode application that asks for your name and then displays a greeting message. This (i.e. a console mode application) is the kind of program that you will build for all your lab and class exercises/assignments because console mode programs are often simpler to build than GUI or Windowed applications.

There are video instructions for downloading various IDEs and creating the correct program type for various IDEs in URCourses. We have included links to those videos here, set to start at the timecode for creating a console application. You can ignore any File I/O instructions you see in the video for now.

• Recommended for Lab and Lecture: replit.com
• Windows 10 Industry Standard (Community Version): Visual Studio Community 2019
• macOS Industry Standard: XCode
• Windows alternative: Code::Blocks

The Code

When you come to the part where you are ready to put C++ code in your project, type this code into the C++ editor:

// FILE:     hello.cpp
// PURPOSE:  An example of a simple I/O stream 

#include <iostream>
#include <string>

using namespace std;

int main()
{
	string name;

	cout << "Please enter your name" << endl;
	
	cin >> name;
	cout << "Hello, " << name << endl;
	return 0;
}

Make sure you type it... it's important to get used to fixing typing mistakes while you work.

Save hello.cpp after you have finished editing it.

Building the hello Project

In order to compile any code in an IDE, you have to create a project. A project holds three major types of information:

1. It remembers all of the source code files that combine together to create one executable. In this simple example, the file hello.cpp will be the only source code file, but in larger applications you often break the code up into several different files to make it easier to understand (and also to make it possible for several people to work on it simultaneously). The project maintains a list of the different source files and compiles all of them as necessary each time you want to create a new executable.
   
   
2. It remembers compiler and linker options particular to this specific application. For example, it remembers which libraries to link into the executable, whether or not you want to use pre-compiled headers, and so on.
   
   
3. It remembers what type of project you wish to build: a console application, a windows application, etc.
   
   

For now we create a very simple project "hello" and use it to compile hello.cpp.

Compile and Build:

1. Compile
   
   Some IDEs allow you to compile your code as a separate step. This simply compiles the source code in one file like hello.cpp and forms an object file (hello.obj or hello.o) for it. It does not perform a link or create an executable, so it is useful only for quickly compiling a file to check for errors.
   Here's how you can compile the file hello.cpp in a few C++ IDEs:
   • In replit --> g++ is the compiler. Type a command like this in the Console panel:

     
                             g++ code_file.cpp -o output_name
                         

     You can then run the resulting executable by typing something like this afterward:

     
                             ./output_name
                         

     For our hello example that's:

     
     g++ hello.cpp -o hello                       
     ./hello
                         

   • In Visual Studio, select Build --> Compile from the main menu.
     
   • In XCode, select Product --> Perform Action -- > Compile "hello.cpp" from the main menu.
     
   • In Code::Blocks, select Build --> Compile current file from the main menu.
   
   
   
2. Build
   
   In replit, you will see a Run ► button.
   
   The Run button does a more complex compile than the one we typed above. It uses the most recent C++ and adds some features. You don't need them. Replit's Run button will also compile and build a program out of ALL the .cpp files in the Files panel.
   Important: In labs 2 to 10 you put all your .cpp for multiple exercises into one repl - Run won't like this. You will have to compile and run separately. We will remind you how in Lab 2.
   
   In other IDE's the same menu that has Compile will also have a Build option.
   Like replit's Run button, build compiles all of the source files in the project that have been modified since the last build, and then links them to create an executable file.
   
   Tip: A C++ project or repl can only Build successfully if there's only one main() function in all the files present.
   
   
3. Auto Compile/Build/Run
   
   For single one program repls and IDE projects, you won't usualy need to compile or build as a separate step. Usually it is good enough to just run the program.
   Beginners using Visual Studio, especially older version, you should be careful to choose Debug --> Start Without Debugging to run the program.
   

When you run in most IDEs, a window will pop up. If errors or warnings are displayed in the Build status window, there is probably an error in the source file. Often, you can double click on these to be taken to the error. Check your source file again for missing semicolons, quotes, or braces or for spelling mistakes and so on.

XCode and replit are a little different. Watch the videos to see what to do!