public class Demo 练习

public class Demo {
public static void main(String args[]) {
double sum = 0, a = 1;
int i = 1;
while (i <= 20) {
sum = sum + a;
i = i + 1;
a = a * (1.0 / i);
}
System.out.println(sum);
}
}

public class SingleNum {
public static void main(String[] args) {
int count = 0;
for (int i = 1; i < 101; i++) {
// 默认是素数
boolean flag = true;
for (int j = 2; j <= Math.sqrt(i); j++) {
if (i % j == 0) {
// 能整除
flag = false;
}
}
if (flag) {
count += 1;
System.out.print(i + ",");
}
}
System.out.println("\n共计" + count + "个素数");
}
}