计算和组合Calculations & Combining Variables

4.1 四则运算4.1 Basic Arithmetic

程序最擅长的事情之一就是算数。C++ 支持你熟悉的四种运算：One of the things programs do best is math. C++ supports the four operations you already know:

4.2 整数除法陷阱4.2 The Integer Division Trap

注意上面表格里除法的结果：10 / 3 等于 3，不是 3.33。Notice the division result above: 10 / 3 equals 3, not 3.33.

这是因为 10 和 3 都是整数（int），整数除整数，结果还是整数，小数部分直接扔掉。This is because 10 and 3 are both integers (int). When you divide an integer by an integer, the result is also an integer — the decimal part is simply thrown away.

int a = 7 / 2;       // a = 3（不是 3.5！小数部分被扔掉了）
double b = 7.0 / 2;  // b = 3.5（只要有一个是小数，结果就是小数）

int result = 9 / 2;

4.3 取余运算4.3 Modulo (Remainder)

% 叫取余（也叫模运算），它算的是除法的余数。% is called modulo (also known as the remainder operator). It gives you the remainder of a division.

int r = 7 % 3;    // r = 1（7 除以 3 等于 2 余 1）
int s = 10 % 5;   // s = 0（10 除以 5 刚好整除，余数为 0）
int t = 8 % 2;    // t = 0（8 是偶数，除以 2 余 0）

4.4 组合变量做计算4.4 Combining Variables in Calculations

变量不只是用来存数字的，还可以用来做计算，把结果存到新变量里：Variables aren't just for storing numbers — you can use them in calculations and store the results in new variables:

int a = 10;
int b = 20;
int total = a + b;    // total = 30
int diff = b - a;     // diff = 10

4.5 机器人实例：轮子走了多远？4.5 Robot Example: How Far Did the Wheel Travel?

来一个真实的例子。你的机器人轮子转了几圈，你想算它走了多远。Here's a real example. Your robot's wheel has spun a few rotations and you want to calculate how far it traveled.

公式很简单：距离 = 圈数 x 周长，而周长 = 2 x 3.14159 x 半径。The formula is simple: distance = rotations x circumference, where circumference = 2 x 3.14159 x radius.

int main() {
    double radius = 5.0;       // 轮子半径 5cm
    double pi = 3.14159;
    double circumference = 2 * pi * radius;  // 周长
    double rotations = 3.0;    // 转了 3 圈
    double distance = rotations * circumference;

    Brain.Screen.print("Distance: %.1f cm", distance);
    return 0;
}

int main() {
    double radius = 5.0;       // 轮子半径 5cm
    double pi = 3.14159;
    double circumference = 2 * pi * radius;  // 周长
    double rotations = 3.0;    // 转了 3 圈
    double distance = rotations * circumference;

    Brain.Screen.print("Distance: %.1f cm", distance);
    return 0;
}

void initialize() {
    pros::lcd::initialize();

    double radius = 5.0;       // 轮子半径 5cm
    double pi = 3.14159;
    double circumference = 2 * pi * radius;  // 周长
    double rotations = 3.0;    // 转了 3 圈
    double distance = rotations * circumference;

    pros::lcd::print(1, "Distance: %.1f cm", distance);
}

运行结果：屏幕显示 Distance: 94.2 cmResult: The screen shows Distance: 94.2 cm

这就是编程的魅力 -- 你只要告诉程序公式和数据，它帮你算出结果。以后轮子换了大小，只需要改 radius 的值就行。This is the power of programming — you just give the program a formula and data, and it calculates the result for you. If you change the wheel size later, you only need to change the radius value.

4.6 写代码练习4.6 Coding Exercise

int main() {
    double radius = 5.0;
    double circumference = 2 * 3.14159 * radius;
    double distance = 3.0 * circumference;
    Brain.Screen.print("Distance: %.1f cm", distance);
    return 0;
}

int main() {
    double radius = 5.0;
    double circumference = 2 * 3.14159 * radius;
    double distance = 3.0 * circumference;
    Brain.Screen.print("Distance: %.1f cm", distance);
    return 0;
}

void initialize() {
    pros::lcd::initialize();
    double radius = 5.0;
    double circumference = 2 * 3.14159 * radius;
    double distance = 3.0 * circumference;
    pros::lcd::print(1, "Distance: %.1f cm", distance);
}