循环：whileLoops: while

6.1 为什么需要循环？6.1 Why Do We Need Loops?

想想你操控机器人的过程：Think about how you control a robot:

1. 读摇杆的值Read the joystick value
2. 根据摇杆值控制电机Control the motors based on the joystick
3. 回到第 1 步，再读一次...Go back to step 1 and read again...

这个过程要一直重复，从比赛开始到比赛结束。你总不能把同样的代码复制一万遍吧？This process needs to keep repeating from the start of the match to the end. You can't copy-paste the same code ten thousand times, right?

这就是循环的用途 — 让一段代码反复执行。That's what loops are for — making a block of code run over and over.

6.2 while 的基本写法6.2 Basic while Syntax

while (条件) {
    // 条件成立时，反复执行这里的代码
}

执行流程：How it works:

1. 检查条件 → 成立？进入大括号执行代码Check the condition → True? Enter the braces and run the code
2. 执行完 → 回到第 1 步，再检查条件When done → Go back to step 1 and check the condition again
3. 条件不成立？ → 跳出循环，继续往下走Condition false? → Exit the loop and continue with the rest of the code

6.3 while(true) — 永远不停6.3 while(true) — Never Stop

true 的意思是"永远成立"，所以 while(true) 就是无限循环 — 永远不会停。true means "always true," so while(true) is an infinite loop — it never stops.

这在机器人程序里非常常见！遥控器操控模式就是一个无限循环：This is extremely common in robot programs! Driver control mode is an infinite loop:

int main() {
    while (true) {
        // 读摇杆，控制电机
        // ...每次循环都执行

        wait(20, msec);  // 休息 20 毫秒
    }
}

int main() {
    while (true) {
        // 读摇杆，控制电机
        // ...每次循环都执行

        wait(20, msec);  // 休息 20 毫秒
    }
}

void opcontrol() {
    while (true) {
        // 读摇杆，控制电机
        // ...每次循环都执行

        pros::delay(20);  // 休息 20 毫秒
    }
}

6.4 有条件的循环6.4 Conditional Loops

while(true) 是永远不停。但有时候你想"做 5 次就停"或"倒计时到 0 就停"。这时候用一个变量来控制：while(true) never stops. But sometimes you want "do it 5 times and stop" or "count down to 0 and stop." Use a variable to control it:

int count = 0;

while (count < 5) {
    // 这里的代码会执行 5 次
    count++;  // count 加 1
}

执行过程：How it runs:

• 第 1 次：count = 0，0 < 5 成立 → 执行，count 变成 11st time: count = 0, 0 < 5 is true → runs, count becomes 1
• 第 2 次：count = 1，1 < 5 成立 → 执行，count 变成 22nd time: count = 1, 1 < 5 is true → runs, count becomes 2
• ...一直到......and so on until...
• 第 5 次：count = 4，4 < 5 成立 → 执行，count 变成 55th time: count = 4, 4 < 5 is true → runs, count becomes 5
• 第 6 次检查：count = 5，5 < 5 不成立 → 跳出循环！6th check: count = 5, 5 < 5 is false → exits the loop!

6.5 实战：屏幕倒计时6.5 Practice: Screen Countdown

让 Brain 屏幕显示 5、4、3、2、1 的倒计时：Make the Brain screen show a countdown from 5, 4, 3, 2, 1:

int main() {
    int countdown = 5;

    while (countdown > 0) {
        Brain.Screen.clearScreen();
        Brain.Screen.setCursor(1, 1);
        Brain.Screen.print("Countdown: %d", countdown);

        wait(1000, msec);  // 等 1 秒
        countdown--;        // 减 1
    }

    Brain.Screen.clearScreen();
    Brain.Screen.setCursor(1, 1);
    Brain.Screen.print("GO!");

    return 0;
}

int main() {
    int countdown = 5;

    while (countdown > 0) {
        Brain.Screen.clearScreen();
        Brain.Screen.setCursor(1, 1);
        Brain.Screen.print("Countdown: %d", countdown);

        wait(1000, msec);  // 等 1 秒
        countdown--;        // 减 1
    }

    Brain.Screen.clearScreen();
    Brain.Screen.setCursor(1, 1);
    Brain.Screen.print("GO!");

    return 0;
}

void opcontrol() {
    int countdown = 5;

    while (countdown > 0) {
        pros::lcd::clear();
        pros::lcd::set_text(1, "Countdown: " + std::to_string(countdown));

        pros::delay(1000);  // 等 1 秒
        countdown--;         // 减 1
    }

    pros::lcd::clear();
    pros::lcd::set_text(1, "GO!");
}

6.6 动手预测6.6 Predict the Output

看下面这段代码，先想想 sum 最后等于多少：Look at the code below and think about what sum equals at the end:

int sum = 0;
int i = 1;

while (i <= 3) {
    sum = sum + i;
    i++;
}

int n = 10;
while (n > 7) {
    n--;
}