Create cpp_running_time.cpp

2025.09.29_cpp_running_time/cpp_running_time.cpp

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+#include <iostream>
+#include <chrono>
+
+int main() {
+    double x = 0.0; 
+    auto start = std::chrono::high_resolution_clock::now();  // 记录开始时间
+    for (long long i = 0; i < 1e10; ++i) {
+        x += 1e-10;   // 模拟一些计算
+    }
+    auto end = std::chrono::high_resolution_clock::now(); // 记录结束时间
+    auto duration = std::chrono::duration_cast<std::chrono::seconds>(end - start); // 计算时间差
+    std::cout << "Running time: " << duration.count() << " s" << std::endl;
+    std::cout << "Result x = " << x << std::endl;
+    return 0;
+}