Conditional Statements

The if statement

An if runs a block of code only when a condition is true:

int temperature = 32;

if (temperature > 30)
{
    Console.WriteLine("It is hot today");
}

The condition must be a bool. C# will not accept a number or a string in its place, which is different from JavaScript and Python.

int count = 5;
// if (count) { }          // error: cannot convert int to bool
if (count > 0) { }         // correct

if and else

else runs when the condition is false:

int age = 16;

if (age >= 18)
{
    Console.WriteLine("You can vote");
}
else
{
    Console.WriteLine("Not yet");
}

else if chains

Test several conditions in order. The first one that is true wins, and the rest are skipped:

int score = 72;

if (score >= 90)
{
    Console.WriteLine("Grade A");
}
else if (score >= 75)
{
    Console.WriteLine("Grade B");
}
else if (score >= 50)
{
    Console.WriteLine("Grade C");
}
else
{
    Console.WriteLine("Fail");
}

Order matters. If you checked score >= 50 first, a score of 95 would print “Grade C” and never reach the A test.

Braces are optional but recommended

A single statement can follow if without braces:

if (age >= 18) Console.WriteLine("Adult");

This is fine for a one liner, but adding a second line later is a well known bug source:

if (age >= 18)
    Console.WriteLine("Adult");
    Console.WriteLine("Welcome");   // always runs, not part of the if

Most teams always use braces. It removes the risk entirely.

Combining conditions

Use && for “both”, || for “either” and ! for “not”:

bool hasTicket = true;
int age = 15;

if (hasTicket && age >= 18)
{
    Console.WriteLine("Enter");
}
else if (hasTicket && age < 18)
{
    Console.WriteLine("Enter with an adult");
}
else
{
    Console.WriteLine("No ticket");
}

When a condition gets long, give it a name. A well named bool reads better than a long expression:

bool isWeekend = day == "Saturday" || day == "Sunday";
bool isOpen = !isWeekend && hour >= 9 && hour < 17;

if (isOpen)
{
    Console.WriteLine("The shop is open");
}

Nested ifs

An if inside another if works, but deep nesting gets hard to read:

if (user != null)
{
    if (user.IsActive)
    {
        if (user.HasPermission)
        {
            Console.WriteLine("Access granted");
        }
    }
}

Early return

Flip the conditions and exit early. The happy path ends up at the bottom, un-indented:

if (user == null) return;
if (!user.IsActive) return;
if (!user.HasPermission) return;

Console.WriteLine("Access granted");

This is called a guard clause and it is one of the most useful habits you can build.

The ternary operator

When an if only chooses between two values, the ternary form is shorter:

int age = 20;
string label = age >= 18 ? "adult" : "minor";
Console.WriteLine(label);   // adult

Do not nest ternaries. Two levels deep is already hard to read.

Comparing strings in conditions

Strings compare by content with ==. For case insensitive checks, use Equals with a comparison option:

string answer = "Yes";

if (answer.Equals("yes", StringComparison.OrdinalIgnoreCase))
{
    Console.WriteLine("Confirmed");
}

Checking for null

Use is null and is not null. They are clearer than == null and cannot be overridden by a badly written class:

string? name = null;

if (name is null)
{
    Console.WriteLine("No name provided");
}

if (name is not null && name.Length > 0)
{
    Console.WriteLine($"Hello {name}");
}

Quick recap

• if needs a real bool, not a number or string.
• else if chains are checked top to bottom, and order matters.
• Always use braces, even for one line, to avoid a classic bug.
• Name complex conditions with a bool variable.
• Guard clauses with early return flatten nested ifs.
• The ternary ? : is for choosing between two values, not for logic.