Tutorial 3: Conditional Logic & Filters

Learn to make decisions in your code with if/else statements and filter collections.

Finished Script: 03_Tutorials/RevitAPI_Fundamentals/03_ConditionalLogic.cs

🎯 What You'll Learn

• if/else statements for decision making
• Comparison operators (>, <, ==, etc.)
• LINQ .Where() for elegant filtering

The if/else Pattern

Make decisions based on conditions:

double length = GetWallLength(wall);

if (length > 5)
{
    Println("This is a long wall");
}
else
{
    Println("This is a short wall");
}

Step 1: Comparison Operators

Operator	Meaning
>	Greater than
<	Less than
>=	Greater than or equal
<=	Less than or equal
==	Equals
!=	Not equals

Step 2: Categorize Elements

Create a wall analyzer that sorts walls by length:

var longWalls = new List<Wall>();
var shortWalls = new List<Wall>();

foreach (var wall in allWalls)
{
    double length = GetWallLength(wall);
    
    if (length > threshold)
    {
        longWalls.Add(wall);
    }
    else
    {
        shortWalls.Add(wall);
    }
}

Println($"Long walls: {longWalls.Count}");
Println($"Short walls: {shortWalls.Count}");

Step 3: Boolean Logic

Combine conditions with && (AND) and || (OR):

// Both conditions must be true
if (length > 3 && length < 10)
{
    Println("Medium wall");
}

// Either condition can be true
if (name.Contains("Exterior") || name.Contains("Curtain"))
{
    Println("Special wall type");
}

Step 4: LINQ Alternative

Instead of loops with if/else, use .Where():

// Traditional approach
var longWalls = new List<Wall>();
foreach (var wall in allWalls)
{
    if (GetLength(wall) > 5)
        longWalls.Add(wall);
}

// LINQ approach (same result, cleaner code)
var longWalls = allWalls.Where(w => GetLength(w) > 5).ToList();

The => is a "lambda expression" - think of it as "where the wall's length is greater than 5".

Step 5: Multiple Categories

Add a third category with else if:

if (length > 10)
{
    Println("Extra long");
}
else if (length > 5)
{
    Println("Long");
}
else if (length > 2)
{
    Println("Medium");
}
else
{
    Println("Short");
}

💡 Try This

1. Add a "Medium Walls" category
2. Filter walls by wall type name (contains "Exterior")
3. Combine length AND height conditions

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Next: Tutorial 4: Bulk Updates →