、分别用+while+语句、do-while+语句、for+语句编写程序，计算+e≈1+1/1!+1/2!+...+1/n!

以下是三种不同的语句实现计算e的程序：

1. while语句实现

int n = 1;
double sum = 1, item = 1;
while (true) {
    item = item / n;
    sum += item;
    n++;
    if (item < 1e-6) {
        break;
    }
}
System.out.println("使用while循环计算的e=" + sum);

2. do-while语句实现

int n = 1;
double sum = 1, item = 1;
do {
    item = item / n;
    sum += item;
    n++;
} while (item >= 1e-6);
System.out.println("使用do-while循环计算的e=" + sum);

3. for语句实现

int n = 1;
double sum = 1, item = 1;
for (int i = 1; item >= 1e-6; i++) {
    item = item / i;    sum += item;
    n = i;
}
System.out.println("使用for循环计算的e=" + sum);