请给出C++代码

草原生态系统仿真是一个较为复杂的模型，需要考虑到许多生态因素和参数。以下是一个简单的草原生态系统模型的C++代码示例，仅供参考：

#include <iostream>
#include <vector>
#include <random>

using namespace std;

// 定义草原生态系统的类
class GrasslandEcosystem {
public:
    GrasslandEcosystem(double t, double w, double p, double g, double f, double r) :
        temperature(t), water(w), precipitation(p), grazing(g), fire(f), reproduction(r) {}

    // 模拟草地生态系统的演化过程
    void simulate(int years) {
        for (int i = 0; i < years; i++) {
            // 计算每个地点的生物量
            for (int j = 0; j < locations.size(); j++) {
                double biomass = locations[j].biomass;
                double temperature_effect = temperature - locations[j].optimal_temperature;
                double water_effect = water - locations[j].optimal_water;
                double precipitation_effect = precipitation - locations[j].optimal_precipitation;
                double growth_rate = locations[j].growth_rate * (1 + temperature_effect * locations[j].temperature_sensitivity
                    + water_effect * locations[j].water_sensitivity + precipitation_effect * locations[j].precipitation_sensitivity);
                double grazing_loss = biomass * grazing;
                double fire_loss = biomass * fire;
                double reproduction_gain = biomass * growth_rate * reproduction;
                locations[j].biomass += reproduction_gain - grazing_loss - fire_loss;
                if (locations[j].biomass < 0) locations[j].biomass = 0;
            }

            // 计算环境参数
            temperature = normal_distribution<double>(20, 5)(rng);
            water = uniform_real_distribution<double>(0, 1)(rng);
            precipitation = normal_distribution<double>(30, 10)(rng);

            // 计算每个地点的火灾概率
            vector<double> fire_probs;
            for (int j = 0; j < locations.size(); j++) {
                double fire_prob = locations[j].biomass * fire * locations[j].fire_sensitivity;
                fire_probs.push_back(fire_prob);
            }

            // 模拟火灾
            for (int j = 0; j < locations.size(); j++) {
                double fire_prob = fire_probs[j];
                if (uniform_real_distribution<double>(0, 1)(rng) < fire_prob) {
                    locations[j].biomass *= (1 - fire);
                }
            }
        }
    }

private:
    // 定义草地上的每个地点的属性
    struct Location {
        double biomass;  // 生物量
        double optimal_temperature;  // 最适温度
        double optimal_water;  // 最适水分
        double optimal_precipitation;  // 最适降水量
        double temperature_sensitivity;  // 温度敏感度
        double water_sensitivity;  // 水分敏感度
        double precipitation_sensitivity;  // 降水量敏感度
        double growth_rate;  // 生长率
        double fire_sensitivity;  // 火灾敏感度
    };

    // 定义草地上的地点列表
    vector<Location> locations = {
        { 100, 20, 0.5, 50, 0.1, 0.01, 0.01, 0.8, 0.2 },  // A地点的属性
        { 200, 25, 0.6, 60, 0.2, 0.02, 0.02, 0.9, 0.1 },  // B地点的属性
        { 150, 18, 0.4, 40, 0.15, 0.03, 0.03, 0.7, 0.3 }   // C地点的属性
    };

    // 定义环境参数
    double temperature;  // 温度
    double water;  // 水分
    double precipitation;  // 降水量

    // 定义草地的参数
    double grazing;  // 放牧率
    double fire;  // 火灾率
    double reproduction;  // 繁殖率

    // 定义随机数生成器
    default_random_engine rng;
};

int main() {
    GrasslandEcosystem ecosystem(20, 0.5, 50, 0.05, 0.01, 0.1);
    ecosystem.simulate(10);
    return 0;
}

以上代码仅仅是一个简单的示例，实际上草原生态系统模型要考虑到更多的生态因素和参数，需要更加详细和精细的模拟和计算。