In Swift, you are allowed to nest an if statement inside another if statement. So when the condition of the outer if statement is true, then only controls can access the nested if statement. Otherwise, the controls skipped the nested if statement and executed the block of code present right after the outer if statement.

You are also allowed to nest an if statement inside an if-else statement or vice-versa. You can also nest as many if statements as you want but try to avoid excessive nesting because it”s hard to maintain if you encounter an error.

Syntax

Following is the syntax of the nested if statement −

if boolean_expression_1{ 
   /* statement(s) will execute if the boolean expression 1 is true */
   If boolean_expression_2{
      /* statement(s) will execute if the boolean expression 2 is true */
   }
}

You can nest else if…else in a similar way as you have nested if statement.

Flow Diagram

The following flow diagram will show how the nested if statement works.

Example

Swift program to demonstrate the use of nested if statements.

import Foundation

var varA:Int = 100;
var varB:Int = 200;

/* Check the boolean condition using if statement */
if varA == 100 {

   /* If the condition is true then print the following */
   print("First condition is satisfied")

   if varB == 200 {
   
      /* If the condition is true then print the following */
      print("Second condition is also satisfied")
   }
}

print("Value of variable varA is (varA)")
print("Value of variable varB is (varB)")

Output

It will produce the following output −

First condition is satisfied
Second condition is also satisfied
Value of variable varA is 100
Value of variable varB is 200

Example

Swift program to find the leap year using nested if-else statements.

import Foundation

let myYear = 2027

// Checking leap year
if myYear % 4 == 0 {
   if myYear % 100 == 0 {
      if myYear % 400 == 0 {
         print("(myYear) is a leap year.")
      } else {
         print("(myYear) is not a leap year.")
      }
   } else {
      print("(myYear) is a leap year.")
   }
} else {
   print("(myYear) is not a leap year.")
}

Output

It will produce the following output −

2027 is not a leap year.

Example

Swift program to check if the given number is positive or negative even or odd number.

import Foundation

let num = -11

// Checking if the given number is positive 
// or negative even or odd number
if num > 0 {
   if num % 2 == 0 {
      print("Positive even number.")
   } else {
      print("Positive odd number.")
   }
} else if num < 0 {
   if num % 2 == 0 {
      print("Negative even number.")
   } else {
      print("Negative odd number.")
   }
} else {
   print("Number is zero.")
}

Output

It will produce the following output −

Negative odd number.