C# If ... Else

C# supports the usual logical conditions from mathematics:
Less than: a < b
Less than or equal to: a <= b
Greater than: a > b
Greater than or equal to: a >= b
Equal to a == b
Not Equal to: a != b
You can use these conditions to perform different actions for different decisions.
C# has the following conditional statements:
Use if to specify a block of code to be executed, if a specified condition is true
Use else to specify a block of code to be executed, if the same condition is false
Use else if to specify a new condition to test, if the first condition is false
Use switch to specify many alternative blocks of code to be executed
Use the if statement to specify a block of C# code to be executed if a condition is 
True.
if (condition) 
{
  // block of code to be executed if the condition is True
}

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate an error.
In the example below, we test two values to find out if 20 is greater than 
18. If the condition is True, print some text:
if (20 > 18) 
{
  Console.WriteLine("20 is greater than 18");
}


Try it Yourself »

We can also test variables:
int x = 20;
int y = 18;
if (x > y) 
{
  Console.WriteLine("x is greater than y");
}


Try it Yourself »

In the example above we use two variables, x and y, 
to test whether x is greater than y 
(using the > operator). As x is 20, and y is 18, and we know that 20 is greater than 18, we print to the screen that "x is greater than y".
Use the else statement to specify a block of code to be executed if the condition is 
False.
if (condition)
{
  // block of code to be executed if the condition is True
} 
else 
{
  // block of code to be executed if the condition is False
}

int time = 20;
if (time < 18) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}
// Outputs "Good evening."
 


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In the example above, time (20) is greater than 18, so the condition is 
False. 
Because of this, we move on to the else condition and print to the screen "Good 
evening". If the time was less than 18, the program would print "Good day".
Use the else if statement to specify a new condition if the first condition is 
False.
if (condition1)
{
  // block of code to be executed if condition1 is True
} 
else if (condition2) 
{
  // block of code to be executed if the condition1 is false and condition2 is True
} 
else
{
  // block of code to be executed if the condition1 is false and condition2 is False
}

int time = 22;
if (time < 10) 
{
  Console.WriteLine("Good morning.");
} 
else if (time < 20) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}
// Outputs "Good evening."
 


Try it Yourself »

In the example above, time (22) is greater than 10, so the first condition is 
False. The next condition, in the  
else if statement, is also 
False, so we move on to the else
condition since condition1 and condition2 is both 
False - and print to the screen "Good 
evening".
However, if the time was 14, our program would print "Good day."
There is also a short-hand if else, which is known as the ternary 
operator because it consists of three operands. It can be used to 
replace multiple lines of code with a single line. It is often used to replace 
simple if else statements:
variable = (condition) ? expressionTrue :  expressionFalse;

Instead of writing:
int time = 20;
if (time < 18) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}


Try it Yourself »

You can simply write:
int time = 20;
string result = (time < 18) ? "Good day." : "Good evening.";
Console.WriteLine(result);


Try it Yourself »

Print "Hello World" if x is greater than y.
int x = 50;
int y = 10;
 (x  y) 
{
  Console.WriteLine("Hello World");
}

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