无法在python中找到素数代码中的错误

Question

n=5;count=2;i=3;j=2;
while (count <= n):
    for j in range (2,i):
            if(i%j == 0):           
                break
    if(j==i):
        print i
        count = count +1
    i = i+1

I am trying to find first n prime numbers but somehow this code doesn't seem to compile. the program is getting stuck at the for loop . I have tried using writing the code in C using the same logic it seem to work fine but as i need large number support python seem to be an obvious choice and thus wanted to run in python. Any help would be great.

Answer 1

range(a, b) goes from a to b-1 .

n=5;count=2;i=3;j=2;
while (count <= n):
    for j in range (2,i):
        if(i%j == 0):           
            break
    if(j==i-1):
        print i
        count = count +1
    i = i+1

I'm betting you had

 int j;
 for(j = 2; j < i; j++) {
 }

So that by the end of the loop for a prime number, j would be i .

Python doesn't overshoot the limit when using range .

Answer 2

This is a good use for the otherwise-obscure syntax of else: keyword following a loop. As others have commented, your test for successful completion of the for loop is off by one.

Instead, try using else to test for successful completion:

for j in range (2,i):
        if(i%j == 0):
            break
else:
    print i
    count = count +1

Answer 3

Your issue is here:

for j in range (2,i):

This checks j=2,3,4....i-1. Thus your code here is never run:

if(j==i):
        print i
        count = count +1

So count never changes. Thus you get an infinite while loop. Change your check to

if(j==i-1):
        print i
        count = count +1

Answer 4

In Python 3, it's print() , not print . The code compiles when you change this line:

        print(i)

You also seem to have an infinite loop, but I'll let you debug that.