If-Else Statements

Vaibhav • September 9, 2025

While simple if statements allow you to execute code when a condition is true, real-world programs often need to choose between two alternative paths: "if this condition is true, do this; otherwise, do that." This is where if-else statements become essential, providing a clean and efficient way to handle binary decisions in your code.

Think of if-else statements like a fork in the road. When you reach the fork, you must choose one path or the other – you cannot take both paths simultaneously, and you cannot avoid making a choice. The if-else statement ensures that exactly one of two code blocks will execute, never both, never neither.

The If-Else Syntax

The if-else statement extends the basic if statement by adding an alternative path of execution. Here's the fundamental syntax:

if (condition)
{
    // Code to execute when condition is TRUE
}
else
{
    // Code to execute when condition is FALSE
}

The flow is straightforward: C# evaluates the condition in the parentheses. If the condition is true, it executes the first code block and skips the else block entirely. If the condition is false, it skips the if block and executes the else block instead.

Here's a practical example that demonstrates this binary choice:

int userScore = 75;
int passingScore = 70;

if (userScore >= passingScore)
{
    Console.WriteLine("Congratulations! You passed the test.");
    Console.WriteLine("Your score: " + userScore);
}
else
{
    Console.WriteLine("You did not pass this time.");
    Console.WriteLine("Required score: " + passingScore + ", Your score: " + userScore);
}

In this example, exactly one message will be displayed. If the user scored 75 or higher, they see the congratulations message. If they scored below 70, they see the failure message. There's no middle ground – it's one or the other.

Understanding Exclusive Outcomes

The power of if-else statements lies in their guarantee of exclusive outcomes. Unlike multiple separate if statements that can all execute independently, an if-else structure ensures that exactly one path is taken.

// Multiple independent if statements (both could execute)
int temperature = 72;

if (temperature > 70)
{
    Console.WriteLine("It's warm today.");
}

if (temperature < 80)
{
    Console.WriteLine("It's not too hot.");
}

// Output: Both messages display!
// "It's warm today."
// "It's not too hot."

// If-else statement (only one executes)
int temperature = 72;

if (temperature > 75)
{
    Console.WriteLine("It's warm today.");
}
else
{
    Console.WriteLine("It's cool or moderate today.");
}

// Output: Only one message displays!
// "It's cool or moderate today."

This exclusive behavior makes if-else statements perfect for situations where you need to choose between two mutually exclusive actions or responses.

Visualizing the Flow

Understanding the execution flow of if-else statements helps you predict how your programs will behave. Here's how the flow works step by step:

1. Evaluate condition - C# checks if the boolean expression is true or false
2. Choose path - Based on the result, pick either the if block or else block
3. Execute chosen block - Run all statements in the selected block
4. Skip alternative block - Completely ignore the other block
5. Continue execution - Move to the code after the entire if-else structure

Console.WriteLine("Before the if-else statement");

int age = 17;

if (age >= 18)
{
    Console.WriteLine("You can vote in elections.");
    Console.WriteLine("Your civic duty awaits!");
}
else
{
    Console.WriteLine("You cannot vote yet.");
    Console.WriteLine("You can vote when you turn 18.");
}

Console.WriteLine("After the if-else statement");

// Output:
// Before the if-else statement
// You cannot vote yet.
// You can vote when you turn 18.
// After the if-else statement

Practical Examples

Example 1: Login Authentication

A common use case for if-else statements is user authentication, where you need to grant or deny access based on credentials:

string enteredPassword = "mySecret123";
string correctPassword = "mySecret123";

if (enteredPassword == correctPassword)
{
    Console.WriteLine("Access granted!");
    Console.WriteLine("Welcome to the system.");
}
else
{
    Console.WriteLine("Access denied!");
    Console.WriteLine("Incorrect password. Please try again.");
}

This example demonstrates the binary nature of authentication: you either have the right credentials (access granted) or you don't (access denied). There's no middle ground.

Example 2: Price Calculation with Discount

double originalPrice = 120.00;
double discountThreshold = 100.00;
double discountRate = 0.10; // 10% discount

if (originalPrice >= discountThreshold)
{
    double discountAmount = originalPrice * discountRate;
    double finalPrice = originalPrice - discountAmount;
    Console.WriteLine("Discount applied!");
    Console.WriteLine("Original price: $" + originalPrice);
    Console.WriteLine("Discount: $" + discountAmount);
    Console.WriteLine("Final price: $" + finalPrice);
}
else
{
    Console.WriteLine("No discount available.");
    Console.WriteLine("Price: $" + originalPrice);
    Console.WriteLine("Spend $" + discountThreshold + " or more for a discount!");
}

Example 3: Number Classification

int number = -15;

if (number >= 0)
{
    Console.WriteLine(number + " is a non-negative number.");
    Console.WriteLine("Non-negative numbers are zero or positive.");
}
else
{
    Console.WriteLine(number + " is a negative number.");
    Console.WriteLine("Negative numbers are less than zero.");
}

Comparing If-Else with Separate If Statements

It's important to understand when to use if-else versus separate if statements. The choice depends on whether the conditions represent mutually exclusive scenarios or independent checks.

// When conditions are mutually exclusive, use if-else:
int accountBalance = 150;

if (accountBalance >= 0)
{
    Console.WriteLine("Account balance is positive or zero.");
}
else
{
    Console.WriteLine("Account balance is negative (overdrawn).");
}
// A balance cannot be both positive and negative simultaneously

// When conditions are independent, use separate if statements:
int testScore = 85;

if (testScore >= 80)
{
    Console.WriteLine("Excellent work!");
}

if (testScore >= 70)
{
    Console.WriteLine("You passed the test.");
}
// Both conditions can be true independently

Avoiding Deep Nesting

While you can nest if-else statements inside other if-else statements, deep nesting quickly becomes difficult to read and maintain. Here's an example of problematic nesting:

// Avoid deep nesting like this:
int score = 85;
bool hasBonus = true;

if (score >= 70)
{
    if (hasBonus == true)
    {
        if (score >= 80)
        {
            Console.WriteLine("Excellent with bonus!");
        }
        else
        {
            Console.WriteLine("Good with bonus!");
        }
    }
    else
    {
        Console.WriteLine("Passed without bonus.");
    }
}
else
{
    Console.WriteLine("Did not pass.");
}

This nested structure is hard to follow and error-prone. In upcoming lessons, we'll learn about else-if chains and other techniques that provide cleaner alternatives for handling multiple related conditions.

Common Patterns and Best Practices

The Guard Pattern

A common pattern using if-else is the "guard" pattern, where you check for invalid conditions first and handle them immediately:

int divisor = 0;
int dividend = 10;

if (divisor == 0)
{
    Console.WriteLine("Error: Cannot divide by zero!");
    Console.WriteLine("Please provide a non-zero divisor.");
}
else
{
    double result = (double)dividend / divisor;
    Console.WriteLine(dividend + " divided by " + divisor + " equals " + result);
}

Clear Variable Names

Using descriptive boolean variables can make your if-else conditions more self-documenting:

int currentTime = 14; // 24-hour format: 2 PM
int businessStart = 9;
int businessEnd = 17;

bool isDuringBusinessHours = (currentTime >= businessStart && currentTime < businessEnd);

if (isDuringBusinessHours)
{
    Console.WriteLine("The business is currently open.");
    Console.WriteLine("Business hours: " + businessStart + ":00 - " + businessEnd + ":00");
}
else
{
    Console.WriteLine("The business is currently closed.");
    Console.WriteLine("Please call during business hours.");
}

Real-World Applications

If-else statements are fundamental to countless real-world applications:

• User Interfaces - Showing different content for logged-in vs. guest users
• E-commerce - Applying discounts or calculating shipping costs
• Games - Determining win/lose conditions or level progression
• Financial Software - Approving or denying transactions
• Security Systems - Granting or restricting access
• Data Processing - Handling valid vs. invalid input

Every time you see software that responds differently to different inputs – from ATM machines to mobile apps – if-else logic is working behind the scenes to make those binary decisions.

Testing Your If-Else Logic

When working with if-else statements, it's important to test both paths to ensure your logic works correctly:

// Test both conditions with different values
int testValue1 = 25;  // Should trigger the if block
int testValue2 = 15;  // Should trigger the else block
int threshold = 20;

// Test case 1
Console.WriteLine("Testing value: " + testValue1);
if (testValue1 > threshold)
{
    Console.WriteLine("Value is above threshold");
}
else
{
    Console.WriteLine("Value is at or below threshold");
}

Console.WriteLine(); // Empty line for readability

// Test case 2
Console.WriteLine("Testing value: " + testValue2);
if (testValue2 > threshold)
{
    Console.WriteLine("Value is above threshold");
}
else
{
    Console.WriteLine("Value is at or below threshold");
}

What's Coming Next

If-else statements handle binary decisions beautifully, but what about situations where you have multiple related conditions to check? In our next lesson on else-if chains, we'll learn how to handle scenarios like grading systems (A, B, C, D, F) or multi-tier pricing structures cleanly and efficiently.

Understanding if-else thoroughly prepares you for these more complex conditional structures, as else-if chains are essentially multiple if-else statements connected together in an elegant way.

Summary

If-else statements provide a clean, efficient way to choose between two mutually exclusive paths of execution. Unlike separate if statements that can execute independently, if-else guarantees that exactly one of two code blocks will run – never both, never neither.

The syntax is straightforward: `if (condition) { ... } else { ... }`. When the condition is true, the if block executes and the else block is skipped. When the condition is false, the else block executes and the if block is skipped.

Use if-else when you have binary decisions or mutually exclusive scenarios. Avoid deep nesting, use descriptive variable names to make conditions self-documenting, and always test both paths to ensure your logic works correctly. These practices will help you write clear, maintainable conditional code that handles real-world decision-making scenarios effectively.