C++ 多维数组

多维数组

多维数组是数组的数组。

要声明多维数组，请定义变量类型，指定数组名称，后跟方括号（指定主数组有多少个元素），后跟另一组方括号（指示子数组有多少个元素）。

string letters[2][4];

与普通数组一样，可以在大括号内插入带有数组文字（逗号分隔的列表）的值。在多维数组中，数组文字中的每个元素都是另一个数组字面量。

string letters[2][4] = {
  { "A", "B", "C", "D" },
  { "E", "F", "G", "H" }
};

数组声明中的每一组方括号都会为数组添加另一个维度。像上面这样的数组称为二维数组。

数组可以有任意数量的维度。数组的维数越多，代码就越复杂。下面的数组有三个维度:

string letters[2][2][2] = {
  {
    { "A", "B" },
    { "C", "D" }
  },
  {
    { "E", "F" },
    { "G", "H" }
  }
};

访问多维数组的元素

要访问多维数组的元素，请在数组的每个维度中指定一个索引号。

此语句访问字母数组第一行（0）和第三列（2）中元素的值。

#include <iostream>
using namespace std;
int main() {
  string letters[2][4] = {
    { "A", "B", "C", "D" },
    { "E", "F", "G", "H" }
  };
  cout << letters[0][2];
  return 0;
}
运行一下

更改多维数组中的元素

要更改元素的值，请引用每个维度中元素的索引

#include <iostream>
using namespace std;
int main() {
  string letters[2][4] = {
    { "A", "B", "C", "D" },
    { "E", "F", "G", "H" }
  };
  letters[0][0] = "Z";
  cout << letters[0][0];
  return 0;
}
运行一下

在多维数组中循环

要在多维数组中循环，数组的每个维度都需要一个循环。

以下实例输出字母数组中的所有元素:

#include <iostream>
using namespace std;
int main() {
  string letters[2][4] = {
    { "A", "B", "C", "D" },
    { "E", "F", "G", "H" }
  };
  for(int i = 0; i < 2; i++) {
    for(int j = 0; j < 4; j++) {
      cout << letters[i][j] << "\n";
    }
  }
  return 0;
}
运行一下

这个例子展示了如何在三维数组中循环:

#include <iostream>
using namespace std;
int main() {
  string letters[2][2][2] = {
    {
      { "A", "B" },
      { "C", "D" }
    },
    {
      { "E", "F" },
      { "G", "H" }
    }
  };
  for(int i = 0; i < 2; i++) {
    for(int j = 0; j < 2; j++) {
      for(int k = 0; k < 2; k++) {
        cout << letters[i][j][k] << "\n";
      }
    }
  }
  return 0;
}
运行一下

为什么是多维数组？

多维数组非常擅长表示网格。这个例子展示了它们的实际用途。在下面的实例中，我们使用多维数组来表示战舰的一个小游戏:

#include <iostream>
using namespace std;
int main() {
  // We put "1" to indicate there is a ship.
  bool ships[4][4] = {
    { 0, 1, 1, 0 },
    { 0, 0, 0, 0 },
    { 0, 0, 1, 0 },
    { 0, 0, 1, 0 }
  };
  // Keep track of how many hits the player has and how many turns they have played in these variables
  int hits = 0;
  int numberOfTurns = 0;
  // Allow the player to keep going until they have hit all four ships
  while (hits < 4) {
    int row, column;
    cout << "Selecting coordinates\n";
    // Ask the player for a row
    cout << "Choose a row number between 0 and 3: ";
    cin >> row;
    // Ask the player for a column
    cout << "Choose a column number between 0 and 3: ";
    cin >> column;
    // Check if a ship exists in those coordinates
    if (ships[row][column]) {
      // If the player hit a ship, remove it by setting the value to zero.
      ships[row][column] = 0;
      // Increase the hit counter
      hits++;
      // Tell the player that they have hit a ship and how many ships are left
      cout << "Hit! " << (4-hits) << " left.\n\n";
    } else {
      // Tell the player that they missed
      cout << "Miss\n\n";
    }
    // Count how many turns the player has taken
    numberOfTurns++;
  }
  cout << "Victory!\n";
  cout << "You won in " << numberOfTurns << " turns";
  return 0;
}
运行一下