0.3.16 Reading a Simple if/else Statement

A simple if statement gives the program one optional block.

An if/else statement gives the program two alternative blocks.

One block runs when the condition is true.

The other block runs when the condition is false.

A simple instructional soccer example is:

if (player1.isAvailable)
{
    System.Console.WriteLine("Include the player in the available list.");
}
else
{
    System.Console.WriteLine("Leave the player off the available list.");
}

Only one of those two blocks runs for a single evaluation of the condition.

The decision still begins here:

if (player1.isAvailable)

Ask:

That value selects the path.

{
    System.Console.WriteLine("Include the player in the available list.");
}

else
{
    System.Console.WriteLine("Leave the player off the available list.");
}

The else does not contain another condition.

It represents the alternative when the if condition was false.

Conceptually:

Is the player available?
       /           \
    true           false
     |               |
Include player    Leave player off

The two branches are alternatives.

The program does not run both branches for the same evaluation of the condition.

Consider:

if (player1.isAvailable)
{
    System.Console.WriteLine("Available");
}
else
{
    System.Console.WriteLine("Unavailable");
}

System.Console.WriteLine("Roster review complete.");

When the condition is true:

• NNew
• CChanged
• RRemoved

When the condition is false:

• NNew
• CChanged
• RRemoved

The branches differ inside the if/else, then execution continues with the shared statement afterward.

This is the same flow pattern you saw in activity diagrams when two paths later rejoined.

An activity diagram might represent:

• NNew
• CChanged
• RRemoved

The C# implementation uses:

if (player1.isAvailable)
{
    System.Console.WriteLine("Available");
}
else
{
    System.Console.WriteLine("Unavailable");
}

The visual model and the source code express the same two-path decision in different forms.

The diagram emphasizes flow.

The C# provides executable instructions.

Suppose the debugger shows:

player1.isAvailable = false

Before stepping over the if, you can predict:

Then use F10 to observe the path.

If Visual Studio moves to the statement in the else block, the runtime evidence matches the prediction.

This is a useful pattern:

Read the condition → predict the branch → observe execution

An if or else block can group several statements.

For example:

if (player1.isAvailable)
{
    System.Console.WriteLine("Available");
    System.Console.WriteLine("Consider for the lineup.");
}
else
{
    System.Console.WriteLine("Unavailable");
    System.Console.WriteLine("Do not include in the lineup.");
}

The braces show which statements belong to each path.

When the condition is true, both statements in the true block run in sequence.

When the condition is false, both statements in the else block run in sequence.

At this stage, focus on simple Boolean conditions.

Do not turn a basic example into a complicated chain of decisions.

The current skill is reading:

• NNew
• CChanged
• RRemoved

More advanced conditional structures appear later.

Keep this distinction clear:

if

Both structures depend on Boolean reasoning.

Both can be predicted from the condition.

Both can be traced in the debugger.

And both can be represented visually with activity-diagram decision paths.