Functions: name reusable work

A report calculation should not be copied for every student. A function groups statements behind a name, accepts inputs and can return a result. Its parameter types and return type make the contract visible before you inspect its body.

What you’ll learn

Call a typed function and use its return value.
Identify the missing zero-count validation in an average calculation.

Functions: name reusable work in the example

1
Call with inputs
A report calculation should not be copied for every student.
```
Call with inputs
```
→2
Compute a result
The func keyword begins a declaration.
```
Compute a result
```
→3
Return to caller
The caller supplies total 155 and count 2 using labels.
```
Return to caller
```

The caller supplies total 155 and count 2 using labels. The function converts both integers and returns 77.5. Assigning that result keeps it available to the caller; the print happens separately afterward.

How functions: name reusable work works

The func keyword begins a declaration. Parameters receive values for each call, and an arrow names the return type. A local constant exists inside that call’s scope. Returning a value differs from printing it: callers can use a returned number in later calculations.

Work through functions: name reusable work

Save this complete program as main.swift and run it with the Swift toolchain. No separate input file is needed.

Swift · complete program

func average(total: Int, count: Int) -> Double {
  return Double(total) / Double(count)
}
let result = average(total: 155, count: 2)
print(result)

Expected output

77.5

Follow the execution

The caller supplies total 155 and count 2 using labels. The function converts both integers and returns 77.5. Assigning that result keeps it available to the caller; the print happens separately afterward.

Try this program in the Swift compiler. Paste the complete source above.

Practice: Functions: name reusable work

Your task: What input must this simple function reject before division?

Swift · complete program

func average(total: Int, count: Int) -> Double {
  return Double(total) / Double(count)
}
let result = average(total: 155, count: 2)
print(result)

Worked answer

It must reject a count of zero for a meaningful average. Add validation or a suitable optional or throwing result, rather than presenting division by zero as a valid report.

Return a value the caller can use

A function body can contain branches, loops and other calls. Scope prevents a local name from automatically becoming available everywhere. Avoid recursion without a stopping case, because repeatedly calling the same function can exhaust resources.

Return a value the caller can use

It must reject a count of zero for a meaningful average. Add validation or a suitable optional or throwing result, rather than presenting division by zero as a valid report. A function body can contain branches, loops and other calls.

Further reading: official Swift language guide.

Reaching the recap and completing the quizzes are separate milestones.

Next lesson: Argument labels, defaults and inout →

Functions: name reusable work