C# if...else Statement

The if...else statement in C# allows you to conditionally execute one block of code or another based on a boolean expression.

Here's the basic syntax of an if...else statement in C#:

if (boolean_expression)
{
    // code to execute if boolean_expression is true
}
else
{
    // code to execute if boolean_expression is false
}

The boolean_expression is any expression that returns a boolean value (true or false). If the boolean_expression is true, the code inside the first block will be executed. Otherwise, the code inside the second block will be executed.

Here's an example of using the if...else statement to determine whether a number is even or odd:

int num = 5;

if (num % 2 == 0)
{
    Console.WriteLine(num + " is even");
}
else
{
    Console.WriteLine(num + " is odd");
}

In this example, if the remainder of num divided by 2 is equal to 0, then the if block will be executed, indicating that num is even. Otherwise, the else block will be executed, indicating that num is odd.

You can also use nested if...else statements to test multiple conditions. For example:

int score = 75;

if (score >= 90)
{
    Console.WriteLine("Grade: A");
}
else if (score >= 80)
{
    Console.WriteLine("Grade: B");
}
else if (score >= 70)
{
    Console.WriteLine("Grade: C");
}
else if (score >= 60)
{
    Console.WriteLine("Grade: D");
}
else
{
    Console.WriteLine("Grade: F");
}

In this example, the program tests the value of score against a series of conditions, printing out the corresponding letter grade based on the score.