Swift Program – Check if given number is Prime Number

In this tutorial, you will learn explore how to write a Swift program to determine whether a given number is a prime number or not.

Swift Program – Prime Number

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself.

Examples for Prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, etc.

How to check if given number is Prime number

To check if a number is prime, we’ll follow these steps:

1. Iterate from 2 to the square root of the number.
2. Check if the number is divisible by any of the integers within the iteration range.
3. If the number is divisible, it’s not a prime number. Otherwise, it is a prime number.

When we are building the while loop condition, we take advantage of the mathematical fact that if there is no number less than i that is not a factor then there is no number greater than n/i that is a factor.

Program

Let’s write a Swift program to determine whether a given number is prime or not. Here’s the program.

main.swift

import Foundation

func isPrime(_ number: Int) -> Bool {
    var n = number
    if n <= 1 {
        return false
    }
    
    var i = 2
    while i <= n/i {
        if n % i == 0 {
            return false
        }
        i += 1
    }
    
    return true
}

print("Enter a number : ", terminator: "")
if let number = Int(readLine()!) {
    if isPrime(number) {
        print("\(number) is a prime number")
    } else {
        print("\(number) is not a prime number")
    }
}

isPrime() function takes a number and returns a boolean value representing whether the given number is a Prime or not.

Output

Conclusion

In this Swift Tutorial, we learned how to determine if a given number is a Prime number using Swift. We used While loop to check if there is a factor other than 1 and given number, between 2 and the given number.