Visual Studio

After this lesson you can

• Explain how a solution, its projects and their files fit together in Visual Studio
• Pause a running program at a breakpoint and step through it with the debugger

Key takeaways

• A project is one program or library, with its settings in a .csproj file. A solution (.slnx) holds the projects that belong together.
• Each exercise in this course is a solution with two projects: your program, and the tests that check your answers.
• Ctrl+F5 builds and runs the startup project, and F5 runs it with the debugger. If the build fails, the Error List shows what's wrong and where.
• A breakpoint pauses your program on a line, so you can see every variable's value, and F10 then runs one line at a time.
• When a program gives a wrong answer, put a breakpoint where things should be right and step forward until a value isn't what you expect.

Visual Studio is the IDE you'll use for C# in this course. It's a large program with hundreds of menus, but you only need a few parts of it to start: where your files live, how to run your program, and how to watch it run, one line at a time.

Solutions and projects

Visual Studio organizes your work in two layers:

• A project is one program or library: its code files, its settings and the libraries it uses. Its settings live in a project file that ends in .csproj.
• A solution is a container for one or more projects that belong together, such as a web app and the tests that check it. Its file ends in .slnx (older solutions use .sln).

When you open a solution, Visual Studio opens every project in it. In this course, each exercise is a solution with two projects: your program, and the tests that check your answers.

VariablesExercise.slnx            the solution
├── VariablesExercise/            a project: your program
│   ├── VariablesExercise.csproj
│   └── Program.cs
└── VariablesExercise.Tests/      a project: the tests
    ├── VariablesExercise.Tests.csproj
    └── AnswerTests.cs

Solution Explorer

Solution Explorer, usually on the right, shows your solution, its projects and their files as a tree. Double-click a file to open it in the editor. Right-click a project to add a file to it, or to choose Set as Startup Project: the project that runs when you press the Run button.

If Solution Explorer has disappeared, open it again from View > Solution Explorer (or press Ctrl+Alt+L).

Running your program

Both kinds of run first build your program: Visual Studio compiles every project the startup project needs. If your code has a mistake the compiler can find, the build fails and the Error List window (View > Error List) shows what's wrong and on which line. Double-click an error to jump to it.

The debugger

A program runs thousands of lines a second, far too fast to watch. The debugger lets you pause it, look at every variable, and move forward one line at a time.

Try it now. You need a project to run, so make a quick one:

1. In Visual Studio, choose File > New > Project (or Create a new project in the start window).
2. Choose Console App (the one marked C#), then Next.
3. Set Project name to DebuggerTry, click Next, then Create.
4. In Solution Explorer, double-click Program.cs and replace its code with this program.

Don't worry about how the code works yet. int[] holds a list of scores, and foreach visits each score in turn. You will learn both in the Arrays and Loops chapter.

int[] scores = { 21, 14, 35, 28 };
int total = 0;

foreach (int score in scores)
{
    total = total + score;
}

Console.WriteLine("Total points: " + total);

Total points: 98

1. Click in the gray margin to the left of the line total = total + score;. A red dot appears: a breakpoint, a place where the program will pause.
2. Press F5. The program starts, and stops on that line before running it. A yellow arrow shows where it is.
3. Hover over total and score to see their values. The Locals window at the bottom shows every variable at once.
4. Press F10 (Step Over) to run one line. Press F5 (Continue) to run until the breakpoint is reached again. Watch total grow: 21, 35, 70, 98.
5. Click the red dot to remove the breakpoint, then press F5 to let the program finish.

When a program gives a wrong answer, the debugger is how you find out why: put a breakpoint where things should be right, and step forward until a value isn't what you expect.

Check yourself

2 questions to try on the lesson page.

So what

Visual Studio does three jobs for you: it keeps your projects organized in a solution, it builds and runs them with one key, and its debugger shows you what your program is really doing, line by line.

Key terms

• Visual Studio
• Solution
• Build
• Debugger
• Breakpoint

Cheat sheets

• Visual Studio