In this workshop you will learn about user-defined functions that return a value to its caller.
| Before you begin, I assume you have done the following: |
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| Figure A: The Xcode project zip file | Figure B: Finder view of the Xcode project |
Functions That Return A Value
If you want a function to return one or more values to its caller, you’ll have to create a user-define function. Such a function has this syntax.
func functionName (argument, argument, ...) -> type {
// Do something
return value
}
The function’s arguments are optional; however it must return a value to its caller. After the arrow ->, you add the function’s return type. It could be any one of Swift’s standard type (String, Char, Double Float, Int, Bool) or a collection type (Array, Dictionary)
Using a Function To Calculate Final Grade
Suppose an English teacher asked you to create an iOS application that calculates her students’ final grades. The app should prompt the teacher for a student’s midterm exam grade and the final exam grade. The final grade is 40 percent of the midterm exam grade plus 60 percent of the final exam grade. The teacher wants the final grade correctly round to the nearest integer. For now, code the application to process one student’s grade. Following is the pseudocode solution for this problem.
calculateGradeButtonTapped()
Prompt for and obtain midterm exam score
Prompt for and obtain final exam score
If (midterm exam score && final exam score is not empty) then
finalGrade = calculateAndReturnFinalGrade(midtermExamScore, finalExamScore)
Display finalGrade
else
Display error message
end if
end
calculateAndReturnFinalGrade(midTermExamScore, finalExamScore)
Calculate the roundedGrade
Return the roundedGrade
end
Coding The ViewController.swift File
To translate above pseudocode into Swift code, you have to first click the ViewController.swift class file to load it in the code editor, then add code shown below in the calculateGradeButtonTapped() function.
@IBAction func calculateGradeButtonTapped(sender: AnyObject) {
// Convert each Text Field type to an optional Int
let midterm: Int? = midtermExamScore.text.toInt()
let final: Int? = finalExamScore.text.toInt()
// Ensure the Text Fields aren't nil before unwrapping them with the ! and calling
// the calculateAndReturnFinalGrade() function
if midterm != nil && final != nil {
var finalGrade: Int = calculateAndReturnFinalGrade(midterm!, finalExamScore:final!)
// Format and display the finalGrade in the label object
outputLabel.text = NSString(format: "Final grade %i", finalGrade)
} else {
// The user entered invalid data in one or both Text Field objects,
// so display an error message in the label object
outputLabel.text = "Only numbers are allowed in the text boxes"
}
}
Next, add code shown below in the calculateAndReturnFinalGrade() function.
func calculateAndReturnFinalGrade(midtermExamScore:Int, finalExamScore:Int) -> Int {
let midtermWeight : Float = 0.40
let finalWeight: Float = 0.60
let grade: Float = midtermWeight * Float(midtermExamScore) + finalWeight * Float(finalExamScore)
let roundGrade: Float = grade + 0.50
return Int(roundGrade)
}
Test The App In The iOS Simulator
After entering above code in the ViewController.swift file, test the application in the iPad or iPhone Simulator. Here are samples of what the app’s user interface will look like on the iPhone 4 Simulator screen, after entering data in the Text Fields and clicking the Calculate Grade button.
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