作为 Python 的第一个练习,我尝试编写一个使用循环来查找素数的程序。一切都适用于 for 循环,所以我尝试使用 while 循环。这可行,但程序返回一些不正确的数字。
import math
# looking for all primes below this number
max_num = int(input("max number?: "))
primes = [2] # start with 2
test_num = 3 # which means testing starts with 3
while test_num < max_num:
i = 0
# It's only necessary to check with the primes smaller than the square
# root of the test_num
while primes[i] < math.sqrt(test_num):
# using modulo to figure out if test_num is prime or not
if (test_num % primes[i]) == 0:
test_num += 1
break
else:
i += 1
else:
primes.append(test_num)
test_num += 1
print(primes)
所以奇怪的是max_num=100
它返回:
[2, 3, 5, 7, 9, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]
除了 9、25 和 49 之外,其他都是正确的,我不明白为什么。