c++ - 无法理解函数

Question

基本上我有一张藏宝图，用户正在尝试寻找宝藏。藏宝图应该是用二维数组打印的。我们应该调用函数来随机化宝藏和开始位置、用户的每一回合等。

我不知道如何在函数中声明变量。我每次编写函数时都必须重新声明，但我的教授说我应该只声明一次？

我的教授编写的主要函数:

int main() 
{
   char Map[ROWS][COLS];
   int TreasureR, TreasureC; 
   int StartR, StartC; 
   int Row, Col;   
   int NumMoves = 0;          // The number of player moves
   bool Winner = false;
   bool Quit = false;

   cout << "This homework was written by Savanna Bruce.\n";
   cout << "You are stranded on a desert island with no idea how to survive.\n";
   cout << "Fortunately, there are tools to survive and a hidden Treasure!\n";
   cout << "Find the Treasure!!!\n\n\n";


   // Seed the random number variable
   srand (time(NULL));

   // Start a New Game or Continue an Old one
   InitMap (Map);

   // Add code to place the treasure and start
   Random();
   // Add code to play the game
   PlayTurn();
   // Print the Map, hide the Treasure
   PrintMap(Map, false);

   return 0;
}

到目前为止我的功能:

// Name: InitMap
// Description: Initialize the Map with all EMPTY cells
// Return: Nothing
// ---------------------------------------------------
void InitMap(char Map[][COLS])
{
    Map = 0;
}
// ---------------------------------------------------
void Random()
{
    int TreasureC, TreasureR;
    int StartC, StartR;
    int Col, Row;

    // Set the location of the treasure chest
    TreasureC = rand() % COLS;   // set to a value in range 0..XDIM-1
    TreasureR = rand() % ROWS;   // set to a value in range 0..YDIM-1

    // Set the starting location of the player
    StartC = rand() % COLS;      // set to a value in range 0..XDIM-1
    StartR = rand() % ROWS;      // set to a value in range 0..YDIM-1
    Col = StartC;
    Row = StartR;
}

void PrintMap(const char Map[][COLS], const bool showTreasure) 
{
    int TreasureR = 0;
    int TreasureC = 0;

    for (int row = 0; row < ROWS; row++)
    {
       for (int col = 0; col < COLS; col++)
       {
           if ((row == TreasureR && col == TreasureC) && showTreasure == true)
               cout << TREASURE;
           else
               cout << EMPTY;
       }
    cout <<  endl;
    }

}

全局变量:

const int FAST = 3;
const int SLOW = 5;
const int COLS = 20;                // For MAP Size
const int ROWS = 10;                // For MAP Size
const int MAX_ROW = ROWS - 1;       // valid locations are 0..ROWS - 1
const int MAX_COL = COLS - 1;       // valid locations are 0..COLS - 1
const string FILENAME = "Map.txt";  // File to save/load Map from

// Cell types - The Map can have any of these
// characters at a location on a Map.
const char START = 'S';
const char PLAYER = 'P';
const char TREASURE = 'T';
const char EMPTY = '*';
const char VISITED = 'X';

有人可以告诉我这些是否正确，以及我是否应该一遍又一遍地声明我的变量？

Answer 1

你的问题是你正在重新声明

int TreasureR, TreasureC; 
int StartR, StartC; 
int Row, Col;   

在main和Random中

只需通过引用 Random() 传递这些值即可解决您的问题:

void Random(int& TreasureC, int& TreasureR, int& StartC, int& startR, int& Col, int& Row)
{
    // Set the location of the treasure chest
    TreasureC = rand() % COLS;   // set to a value in range 0..XDIM-1
    TreasureR = rand() % ROWS;   // set to a value in range 0..YDIM-1

    // Set the starting location of the player
    StartC = rand() % COLS;      // set to a value in range 0..XDIM-1
    StartR = rand() % ROWS;      // set to a value in range 0..YDIM-1
    Col = StartC;
    Row = StartR;
}

对 PrintMap 函数执行相同的操作。

您应该查看 understanding variable scope 上的教程。也就是说，当您声明一个变量时，它仅“存在”一定时间(通常在 {} 之间)。当您在 main 内部声明这些变量时，它们不会神奇地存在于您的函数中。您应该声明它们一次，然后将它们传递给需要它们的函数。

您的InitMap()函数实际上应该迭代矩阵中的所有单元格并将它们设置为某些值。 Map = 0 不会这样做。您需要像在 PrintMap

中那样循环遍历行和列

最后，在 Random() 中，虽然您确实在计算行和列，但您实际上并没有在 Map 中“放入”任何内容。按照您的做法，您实际上并不需要 Map 数据结构；您只需使用 Map 数据结构即可。您可以只选择一个宝藏行和列，然后按原样使用您的 PrintMap() 函数。