C# - Decision Making

C# - Decision Making

Decision-making structures are the bedrock of programming logic. They allow your program to evaluate conditions and execute different blocks of code based on whether those conditions are true or false. This enables dynamic and responsive application behavior.

The fundamental flow of decision-making is:

1. Test a condition.
2. If the condition is TRUE, execute a specific block of code.
3. If the condition is FALSE, execute a different block of code (or do nothing).
4. Continue with the rest of the program.

Conditional Statements in C#

C# provides a powerful set of statements for handling conditional logic.

Statement	Description
if	Executes a block of code if a specified condition is true.
if…else	Executes one block of code if the condition is true, and another if it’s false.
if…else if…else	Tests a series of conditions in order and executes the first one that is true.
switch	Selects one of many code blocks to be executed based on a pattern match with an expression.
Ternary Operator (?:)	A shorthand for an if...else statement that returns a value.

The if, else if, and else Statements

These are the most common decision-making statements. They are used to control program flow based on one or more boolean conditions.

Example

This example checks the current temperature and provides different feedback. Notice the clear logic and corrected condition in the else if block.

using System;

public class WeatherReport
{
    public static void Main()
    {
        int temperature = 20;

        if (temperature < 0)
        {
            Console.WriteLine("It's freezing outside!");
        }
        else if (temperature < 15)
        {
            Console.WriteLine("It's a cold day. Wear a jacket.");
        }
        else if (temperature >= 15 && temperature < 25)
        {
            Console.WriteLine("The weather is pleasant.");
        }
        else // temperature >= 25
        {
            Console.WriteLine("It's a hot day. Stay hydrated!");
        }

        Console.WriteLine($"Execution complete. Current temperature was: {temperature}°C");
    }
}

If you compile and execute the code with temperature = 20, the result is:

The weather is pleasant.
Execution complete. Current temperature was: 20°C

The switch Statement and Switch Expressions

The switch statement is ideal when you have a single variable or expression to test against multiple possible values. Modern C# has significantly enhanced the switch statement with pattern matching and introduced a more concise switch expression.

Example: Classic switch Statement

using System;

public class DayOfWeekPrinter
{
    public static void PrintDay(int day)
    {
        switch (day)
        {
            case 1:
                Console.WriteLine("Monday");
                break;
            case 2:
                Console.WriteLine("Tuesday");
                break;
            case 3:
                Console.WriteLine("Wednesday");
                break;
            case 4:
                Console.WriteLine("Thursday");
                break;
            case 5:
                Console.WriteLine("Friday");
                break;
            case 6:
            case 7:
                Console.WriteLine("It's the Weekend!");
                break;
            default:
                Console.WriteLine("Invalid day number!");
                break;
        }
    }
}

Example: Modern switch Expression (C# 8.0+)

Switch expressions provide a more functional and less verbose syntax, which is perfect for assigning a value based on a condition.

public static string GetDayName(int day)
{
    string dayName = day switch
    {
        1 => "Monday",
        2 => "Tuesday",
        3 => "Wednesday",
        4 => "Thursday",
        5 => "Friday",
        6 or 7 => "Weekend", // 'or' pattern
        _ => "Invalid day"   // _ is the discard/default case
    };
    return dayName;
}

Example: switch with Pattern Matching (C# 9.0+)

Pattern matching allows switching on types and property values, making it incredibly powerful.

public decimal CalculateToll(object vehicle)
{
    return vehicle switch
    {
        Car c when c.Passengers == 0 => 2.00m + 0.50m, // Car with no passengers
        Car c when c.Passengers == 1 => 2.00m,
        Car c when c.Passengers == 2 => 2.00m - 0.50m,
        Car _ => 2.00m - 1.00m, // Any other car
        Taxi t => 3.50m,
        Bus b => 5.00m,
        { } => 4.00m, // Any other non-null object
        null => throw new ArgumentNullException(nameof(vehicle))
    };
}

// Dummy classes for the example
public class Car { public int Passengers { get; set; } }
public class Taxi { }
public class Bus { }

The Ternary Conditional Operator (?:)

The ternary operator is a compact, inline if-else statement. It takes three operands: condition ? value_if_true : value_if_false.

Example

int userAge = 21;

// Using if-else
string status;
if (userAge >= 18)
{
    status = "Adult";
}
else
{
    status = "Minor";
}

// Using the ternary operator - much more concise
string ternaryStatus = userAge >= 18 ? "Adult" : "Minor";

Console.WriteLine($"Status from if-else: {status}");
Console.WriteLine($"Status from ternary: {ternaryStatus}");

Best Practices

• Clarity is Key: Prefer if-else for complex logic blocks. Use the ternary operator only for simple, short assignments.
• Avoid Deep Nesting: Deeply nested if statements are hard to read and debug. Refactor them into separate methods or use a different control structure.
• Use switch for Multiple Values: If you are comparing a single variable against 3 or more constant values, a switch statement or expression is often cleaner than a long if-else if chain.
• Embrace Pattern Matching: For modern C# development, learn and use pattern matching with switch. It can dramatically simplify complex conditional logic.