A real value assigns to a parameter in the function’s definition for default parameters. In the function call, a parameter with a default value does not require an argument to pass into it.

Let’s look at an example of a default parameter in action. Let’s pretend we’re writing a programme that computes the total bill amount with a 30% (0.3) discount:

func Discount(totalBill: Double, discount: Double = 0.3) -> Double {
 return totalBill + (totalBill * discount) ;
}

discount is the default parameter in the function Discount(totalBill:discount:).

A default parameter is created in the same way as a regular parameter, with the exception that it is preceded by an assignment operator (=) and a default value.
The parameter type should be the same data type as the default value.

We can omit the discount parameter entirely when calling the function, and the program will use the default value of 0.3 instead of discount in the function body:

print(Discount(totalBill: 500)) ;
 
// Prints: 150.0

If we want to use a different discount, such as 40% instead of 30%, we can call the function and pass in the new discount argument:

print(Discount(totalBill: 500, discount: 0.4)) ;
 
// Prints: 200.0

The new discount parameter value of 0.4 will override the default value set in the function definition and return the result of the expression (500 * 0.4).

Helpful Tools:

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Online Swift Compiler

Official Swift Documentation

Setting up an IDE (Integrated Development Environment) can be difficult for beginners. The Online Compiler will enable you to run your code inside your browser without the need to install an IDE. If you need a more detailed explanation of a specific topic, the best place to find answers is in the Official Documentation.