Java while循环打印平方数不能使用int吗？

Question

In Java, create a do-while loop that starts at 2, and displays the number squared on each line while the number is less than 1,000,000. And this is what I have:

int k = 2;
do {
    System.out.println(k);
    k *= k;
} while(k < 1000000);

The problem is the output, somehow it is getting stuck at 0 and infinitely looping through 0 to print those out? I don't believe it is due to the fact that the number is out of int range, since a 32 bit number's range is around +/- 2 billion... But when I switch up the data type of k to be long everything works fine... Why is this?

Answer 1

It really is due to int . The sequence produced this way is

2
4
16
256
65536
0

And then it remains zero. Note that it never rises above 1000000.

With a long , the number after 65536 would be 4294967296 (which does not fit in an int , but does fit in a long ), so it stops.

This is perhaps more obvious in hexadecimal, the sequence then reads (with sufficiently long integers)

2
4
0x10
0x100
0x10000
0x100000000

An int can only keep the lowest 8 hexadecimal digits, so 0x100000000 becomes 0.

Answer 2

如果要查找2的幂，则需要用k+=1替换k*=k ，并用print(k*k)替换print(k)以2为底的幂运算比二次幂增长快得多，这导致平方超出范围。

Answer 3

Your code to print squares should be

int k = 2;
do {
    System.out.println(k*k);
    k++;
}while(k < 1000000);

As you are storing the result in same variable, your output is growing exponentially