Java循环无限运行

Question

I am doing a factorial question with java loop, it asks 1+1/2!+1/3!+...+1/n!, n is positive, I am using "while" to make it, but the code is run with nothing ：

    public static void main(String[] args) {

    double sum=0,a=1;
    int n=Integer.parseInt(args[0]);
    while(n>0){

        a=a*n;
        sum=sum+1.0/a;
    }
    System.out.print(sum);

}

please help：）

Answer 1

while(n>0){
    a=a*n;
    sum=sum+1.0/a;
}

When do you change n ? You don't. The condition will be always satisfied and you'll never exit the loop. Consider changing the value of n in the body of the loop.

 Iteration |   n
-----------+--------
     1     |   n      > 0 ? Yes
     2     |   n      > 0 ? Yes
     3     |   n      > 0 ? Yes
    ...    |
    ...    |
  Forever  |   n      > 0 ? Yes

Answer 2

As others have pointed out, your original while loop never ends, because the value of n never changes, meaning that the while condition will always be true (assuming the original value was greater than zero).

Is this possibly what you are trying to achieve?

public static void main(String[] args)
{
    double sum = 0, a = 1;
    int n = Integer.parseInt(args[0]);
    for ( int i = 1; i <= n; i++ )
    {
        a *= i;
        sum = sum + (1.0 / a);
    }
    System.out.print(sum);
}

Answer 3

Your code is equal to :

while(true){

    a=a*n;
    sum=sum+1.0/a;
}

You don't change n value , n must be <=0 to break your loop .

Answer 4

Why not try a for loop let's say

public static void main(String[] args) {

    double sum=0;
    int  n=Integer.parseInt(args[0]);
    for(double a=1;a<=n;a++){

        sum=sum+1.0/a;
    }
    System.out.print(sum);

}