模块课程（1/2）
数组和向量
In C++, managing collections of data is primarily done through two tools: old-style arrays (C-style arrays) and vectors (std::vector). Understanding the difference between static and dynamic memory is fundamental to writing efficient code.
1. Static Arrays (C-style Arrays)
An array is a collection of elements of the same type stored in contiguous memory locations. The size of a static array must be known at compile time and cannot be changed later:
int grades[5] = {18, 22, 25, 28, 30}; // Array of 5 integers
Key Characteristics:
- Fixed Size: You cannot add or remove elements at runtime.
- Stack Allocation: Very fast to allocate and deallocate.
- Access: Done via the index operator
[](e.g.,grades[0]for the first element).
2. Dynamic Vectors (std::vector)
The C++ Standard Template Library (STL) provides the std::vector class, which represents a dynamic array. To use it, you must include the <vector> header:
#include <vector>
std::vector<int> numbers; // Creates an empty vector of integers
Common Operations:
- Append to End: The
.push_back(value)method inserts an element at the end of the vector, automatically reallocating memory if needed. - Size: The
.size()method returns the number of elements currently in the vector. - Safe Access: In addition to the
[]operator, you can use the.at(index)method (e.g.,numbers.at(0)), which throws an exception if the index is out of bounds.
std::vector<int> scores = {90, 85};
scores.push_back(95); // scores now contains {90, 85, 95}
std::cout << scores.size(); // Prints 3
Try it yourself
Declare a std::vector of integers named numbers. Add the values 10, 20, and 30 inside it using the .push_back() method, then print its size using numbers.size().
显示提示
Declare the vector with `std::vector<int> numbers;`, insert the three numbers with `.push_back(value)`, and print it with `std::cout << numbers.size();`.
3 次尝试后可用的解决方案
In main, a grades array of 5 elements is defined. Write a for loop to calculate the sum of all elements in the array, store it in the variable sum, and print it using std::cout.
显示提示
Use a `for (int i = 0; i < 5; ++i)`loop and sum each element inside the loop with`sum += grades[i];`.
3 次尝试后可用的解决方案
What is the correct method to append an element to the end of a std::vector in C++?
std::vector<int> numbers; // come aggiungere il valore 50?