The if statement is the most basic and fundamental type of conditional in Swift. It is used to execute some code when a given condition is true.

The structure of an if statement is:

if condition {
  this code will run if condition is true
}

• The if keyword is followed by a condition whose value must be true or false.
• The condition is immediately followed by a code block.
• A code block is a snippet of code enclosed in a pair of curly braces, { }.
• The code block is executed only when the condition is true.
• If the condition is false, the code block does not run.

Suppose we’re creating an app that includes an authentication process. We’d declare the variable, isLoggedIn to be true and set up the following if statement that prints a message to users who are logged in:

var isLoggedIn = true

if isLoggedIn {
  print("Welcome back!")
}

Since the value of the condition is true, the message, Welcome back! will get printed. If isLoggedIn was false, thus our condition false, the code block wouldn’t execute and nothing would get printed.