Python Program to Check Prime Number

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Way 1 – Using for else

In [1]:
number = int(input("Please enter a number : "))

if number > 1:
    for i in range(2, number):
        if number % i == 0:
            print("Number is not prime.")
            break
    else:
        print("Number is prime.")
else:
    print("Number is not prime.")

Please enter a number : 7
Number is prime.

In this approach, we use for else statement to check whether a number is prime or not. Here, the else block will execute only if the for loop completes it all iterations.

Way 2 – Using flag variable

In [1]:
number = int(input("Please enter a number : "))
flag = False

for i in range(2, number):
    if number % i == 0:
        flag = True
        break
        
if flag:
    print("Number is not prime.")
else:
    print("Number is prime.")
        

Please enter a number : 5
Number is prime.

Instead of using for else, here we will use the flag variable, which is false by default and if number got divides by any other number then, it will turn True.

Way 3 – Using While Loop

In [1]:
number = int(input("Please enter a number : "))


if number > 1:
    i = 2
    while i < number:
        if number % i == 0:
            print("Number is not prime.")
            break
        i += 1
    else:
        print("Number is prime.")
else:
    print("Number is not prime.")

Please enter a number : 8
Number is not prime.

While loop can also be used to check whether the number is prime or not. Make sure we have to increment the counter variable inside the while loop.

Programs
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