用于打印 3 的倍数的 while 循环

Question

Your program should print the following:

 0 3 6 9 12 15 18 loop ended!

This is my code. May I know why can't I do the desired output?

int i = 0;

while(i%3 == 0 && i < 20 ) {
    System.out.print(i);
    i++;
}

System.out.print("loop ended!");

Answer 1

You have a condition in your while loop that must be satisfied for the while loop to continue running. When i increments to 1, the while loop condition fails and thus will stop running, so your program will only print 0. You instead should use an if statement inside the while loop with the mod condition:

int i = 0;
while(i < 20) {
    if(i%3 == 0) {
        System.out.print(i + " ");
    }
    i++;
}
System.out.print("loop ended!");

Answer 2

i % 3 == 0 && i < 20 - this condition evaluates to false when the value of i becomes 1. So loop only executes once.

You just need i < 20 as a loop condition and in each iteration of the loop, just add 3 in i .

int i = 0;

while(i < 20) {
   System.out.print(i + " ");
   i += 3;
}

System.out.print("loop ended!");

Output:

0 3 6 9 12 15 18 loop ended!

Answer 3

public static void main(String... args) {
    int i = 0;

    do {
        System.out.print(i + " ");
    } while ((i += 3) < 20);

    System.out.print("loop ended!");
}

---

I offer to simplify your code with usein for loop:

public static void main(String... args) {
    for (int i = 0; i < 20; i += 3)
        System.out.print(i + " ");

    System.out.print("loop ended!");
}