Thursday, October 31, 2019

Python Program to Display Prime Numbers

In this post we'll see a Python program to display prime numbers in the given range. This program helps in understanding usage of nested loops and it also shows a use case where for loop with else in Python can be used.

A number is a prime number if it can be divided either by 1 or by the number itself. So every number with in the given range has to be divided in a loop from 2 till number/2 to check if number is a prime number or not. You only need to run your loop from 2 to N/2 (where N is the current number in the passed range), as no number is completely divisible by a number more than its half. Reducing the iteration to N/2 makes your program to display prime numbers more efficient.

Displaying prime numbers Python program

def display_prime(lower, upper):
    for num in range(lower, upper+1):
        # instead of int(num/2), num//2 (floor division) can also be used
        for i in range(2, int(num/2)+1):
            # if number is completely divisible then it
            # it is not a prime number so break out of loop
            if num % i == 0:
                break
        # if loop runs completely that means a prime number
        else:
            print(num)


def get_input():
    """Function to take user input for display range"""
    start = int(input('Enter start number for displaying prime numbers:'))
    end = int(input('Enter end number for displaying prime numbers:'))
    # prime numbers start from 2
    if start <= 1:
        start = 2
    # call function to display prime numbers
    display_prime(start, end)

# start program
get_input()

Output

Enter start number for displaying prime numbers:40
Enter end number for displaying prime numbers:100
41
43
47
53
59
61
67
71
73
79
83
89
97 

That's all for this topic Python Program to Display Prime Numbers. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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