查找素数和素数的计数-Python

Question

I a beginner at Python, still a tad confused about it. I got to print out the prime numbers but now I am stuck trying to get the count of outputed prime numbers, please help.

import math

n= int (input("Enter an Integer: "))

for j in range(2, n+1):
    if all(j%i!=0 for i in range(2,int(math.sqrt(j))+1)):
        print (j)



    count = 0
    for j in range(2, n+1):
        if j is True:
            len(j)
            print(str(len(j)))

Answer 1

I'll assume that your aim is to print all the prime numbers between 0 and n (Taken as input by the user) and count them. All you have to do is declare 'count' before the first loop and increment it everytime a prime number is found. The code will look something like this :

import math

n= int (input("Enter an Integer: "))
count = 0
for j in range(2, n+1):
    if all(j%i!=0 for i in range(2,int(math.sqrt(j))+1)):
        print (j)
        count = count + 1
print (" Number of prime numbers is : " , count)

What is wrong in your code is that, in the second loop for j in range(2, n+1): , j is an integer and if j is True: is always false, as j is not a 'boolean' value. Hence print(str(len(j))) is never executed.

Answer 2

All you have to do is add a counter in your code. Please go through the code below to see how that can be done.

import math

n= int (input("Enter an Integer: "))
count = 0
for j in range(2, n+1):
    if all(j%i!=0 for i in range(2,int(math.sqrt(j))+1)):
        print (j)
        count = count + 1

print "Number of prime numbers between 1 and " + str(n) + " is " + str(count)