C# - Nested If

C# - Nested `if` Statements

In C#, it is perfectly valid to place an if or if-else statement inside another if or else block. This is called nesting. Nested if statements are used to test for a secondary condition only if the primary condition is true.

Syntax

The basic syntax for a nested if statement is as follows:

if (primary_condition)
{
    // Code to execute if primary_condition is true

    if (secondary_condition)
    {
        // Code to execute if both primary_condition and secondary_condition are true
    }
}

You can also nest if-else and else if statements to handle more complex scenarios.

Example: Basic Nested `if`

This example checks if a number is positive, and if so, it then checks if it is an even number.

int number = 10;

// Primary condition: Check if the number is positive
if (number > 0)
{
    Console.WriteLine("The number is positive.");

    // Nested condition: Check if the number is even
    if (number % 2 == 0)
    {
        Console.WriteLine("And it is also an even number.");
    }
    else
    {
        Console.WriteLine("And it is an odd number.");
    }
}
else
{
    Console.WriteLine("The number is not positive.");
}

// Output:
// The number is positive.
// And it is also an even number.

Example: Nested `else-if` for Grading

Here, we use nested logic to provide more detailed feedback on a student’s grade.

int marks = 85;

if (marks >= 90)
{
    Console.WriteLine("Grade: A+");
}
else if (marks >= 80)
{
    Console.WriteLine("Grade: A");

    // Nested check for high-A performance
    if (marks >= 85)
    {
        Console.WriteLine("Excellent Performance!");
    }
    else
    {
        Console.WriteLine("Good Job!");
    }
}
else if (marks >= 70)
{
    Console.WriteLine("Grade: B");
}
else
{
    Console.WriteLine("Grade: F - Needs Improvement");
}

// Output:
// Grade: A
// Excellent Performance!

Best Practices and Alternatives

While nested if statements are powerful, they can quickly become hard to read and maintain if they go too deep. This is often called the “Arrow Anti-pattern” because the code begins to look like an arrowhead ->.

1. Use Guard Clauses

A guard clause is a check at the beginning of a method that exits early if a condition isn’t met. This reduces nesting and keeps the main logic at the top level.

// --- BEFORE: Nested ---
public void ProcessOrder(Order order)
{
    if (order != null)
    {
        if (order.IsVerified)
        {
            if (!order.IsShipped)
            {
                // Main logic here...
                Console.WriteLine("Processing the order...");
            }
        }
    }
}

// --- AFTER: Using Guard Clauses ---
public void ProcessOrder(Order order)
{
    if (order == null) return;
    if (!order.IsVerified) return;
    if (order.IsShipped) return;

    // Main logic is now clean and un-nested
    Console.WriteLine("Processing the order...");
}

2. Combine Conditions with Logical Operators

If the logic allows, you can combine conditions using && (AND) to flatten the structure.

// Instead of nesting...
if (user.IsAuthenticated)
{
    if (user.HasPermissions)
    {
        // ...
    }
}

// Combine the conditions
if (user.IsAuthenticated && user.HasPermissions)
{
    // ...
}

3. Use a `switch` Expression (C# 8.0+)

For complex conditional logic based on multiple states, a switch expression can be more readable than a deeply nested if-else chain.

// Using a tuple to check multiple conditions at once
string GetWeatherDescription(bool isRaining, int temperature)
{
    return (isRaining, temperature) switch
    {
        (true, < 0) => "Freezing rain. Stay inside!",
        (true, _) => "It's raining.",
        (false, > 30) => "It's hot and sunny.",
        (false, < 10) => "It's cold but dry.",
        _ => "It's a pleasant day."
    };
}

Console.WriteLine(GetWeatherDescription(true, -5)); // Output: Freezing rain. Stay inside!
Console.WriteLine(GetWeatherDescription(false, 35)); // Output: It's hot and sunny.

C# - Nested If

C# - Nested if Statements