diff --git a/website/README.md b/website/README.md index 895e4f0..cb47dcd 100644 --- a/website/README.md +++ b/website/README.md @@ -16,6 +16,254 @@ use `git lfs` for tracking binary types. ```bash $ git lfs track "*.psd" git add .gitattributes + +36% off +Learn to code by doing. Try hands-on Python with Programiz PRO. Claim Discount Now +Programiz +Courses +Tutorials +Examples + +Search tutorials & examples +Try +Programiz PRO + +Learn Python Interactively +Python Examples +Check if a Number is Positive, Negative or 0 +Check if a Number is Odd or Even +Check Leap Year +Find the Largest Among Three Numbers +Check Prime Number +Print all Prime Numbers in an Interval +Find the Factorial of a Number +Display the multiplication Table +Python Tutorials +Python break and continue +Python while Loop +Python for Loop +Python if...else Statement +Python Operators +Python Functions +Python Program to Check Prime Number +To understand this example, you should have the knowledge of the following Python programming topics: + +Python if...else Statement +Python for Loop +Python break and continue +Learn Python with Challenges +Solve challenges and become a Python expert. + + +A positive integer greater than 1 which has no other factors except 1 and the number itself is called a prime number. 2, 3, 5, 7 etc. are prime numbers as they do not have any other factors. But 6 is not prime (it is composite) since, 2 x 3 = 6. + +Example 1: Using a flag variable +# Program to check if a number is prime or not + +num = 29 + +# To take input from the user +#num = int(input("Enter a number: ")) + +# define a flag variable +flag = False + +if num == 1: + print(num, "is not a prime number") +elif num > 1: + # check for factors + for i in range(2, num): + if (num % i) == 0: + # if factor is found, set flag to True + flag = True + # break out of loop + break + + # check if flag is True + if flag: + print(num, "is not a prime number") + else: + print(num, "is a prime number") +Run Code +Output + +29 is a prime number +In this program, we have checked if num is prime or not. Numbers less than or equal to 1 are not prime numbers. Hence, we only proceed if the num is greater than 1. + +We check if num is exactly divisible by any number from 2 to num - 1. If we find a factor in that range, the number is not prime, so we set flag to True and break out of the loop. + +Outside the loop, we check if flag is True or False. + +If it is True, num is not a prime number. +If it is False, num is a prime number. +Note: We can improve our program by decreasing the range of numbers where we look for factors. + +In the above program, our search range is from 2 to num - 1. + +We could have used the range, range(2,num//2) or range(2,math.floor(math.sqrt(num)+1)). The latter range is based on the fact that a composite number must have a factor less than or equal to the square root of that number. Otherwise, the number is prime. + +You can change the value of variable num in the above source code to check whether a number is prime or not for other integers. + +In Python, we can also use the for...else statement to do this task without using an additional flag variable. + +Example 2: Using a for...else statement +num = 407 + +# To take input from the user +#num = int(input("Enter a number: ")) + +if num == 1: + print(num, "is not a prime number") +elif num > 1: + # check for factors + for i in range(2,num): + if (num % i) == 0: + print(num,"is not a prime number") + print(i,"times",num//i,"is",num) + break + else: + print(num,"is a prime number") + +# if input number is less than +# or equal to 1, it is not prime +else: + print(num,"is not a prime number") +Run Code +Output + +407 is not a prime number +11 times 37 is 407 +Here, we have used a for..else statement to check if num is prime. + +It works on the logic that the else clause of the for loop runs if and only if we don't break out the for loop. That condition is met only when no factors are found, which means that the given number is prime. + +So, in the else clause, we print that the number is prime. + +Share on: +Did you find this article helpful? +Related Examples +Python Example + +Print all Prime Numbers in an Interval + +Python Example + +Find the Factorial of a Number + +Python Example + +Find the Factors of a Number + +Python Tutorial + +Python break and continue + + +Join our newsletter for the latest updates. +Enter Email Address +Join + + +Tutorials +Python 3 Tutorial +JavaScript Tutorial +SQL Tutorial +HTML Tutorial +R Tutorial +C Tutorial +C++ Tutorial +Java Tutorial +Rust Tutorial +Go Tutorial +Kotlin Tutorial +Swift Tutorial +C# Tutorial +DSA Tutorial +Examples +Python Examples +JavaScript Examples +C Examples +Java Examples +Kotlin Examples +C++ Examples +Company +About +Advertising +Privacy Policy +Terms & Conditions +Contact +Blog +Careers +Youtube +Apps +Learn Python +Learn C Programming +Learn Java +© Parewa Labs Pvt. Ltd. All rights reserved. + + +