c - 定义变量与初始化

Question

因此，我的教授让我相信，在声明数组的大小时，最好使用 #define 而不是仅将其声明为普通整数。这是正确的吗？

如果是这样，为什么？

另外，如果这是正确的，我做错了什么？当我尝试这样做时，我收到一条消息:

error: expected ';', ',' or ')' before numeric constant

每次我调用数组时。如果我只是将其初始化为整数，该代码就可以工作。

定义和使用可以看下面的代码:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define handsize 5
#define size 52

// Create function prototypes
void create_deck (int deck[]);
void shuffle_deck (int size, int deck[]);
void display_card (int card);
void display_hand (int size, int hand[]);
int popCard (int *size, int deck[]);
int findScore (int size, int hand[]);

int main()
{
    // declare/ initialize variables
    int c, d, p, win = 0, lose = 0 , tie = 0, /*handsize = 0, size = 52,*/ deck[size], hand[handsize], dealer[handsize];
    char play;
    srand(time(NULL));      // attach random number generator to time function for truly random variables

    // explain program to user and ask if they want to play
    printf("This program is a card game that adds the values of all the\n");
    printf("cards in the players hand, and the computers hand. The highest hand wins.\n");
    printf("Would you like to play? Please press 'y' for yes, any other key for no.\n");
    scanf("%c", &play);     // if the user wants to play, continue the program

    // while loop that continues as long as the user wants to play
    while (play == 'y'){

        // call functions to create and shuffle the deck
        create_deck(deck);
        shuffle_deck (size, deck);

        // for loop that calls the popCard function to deal the top card in the deck
        for (c = 0; c < 5; c++){
            hand[c] = popCard (&size, deck);        // player gets a card
            dealer[c] = popCard (&size, deck);      // computer gets a card
            handsize++;
            // call the display_hand function to display the individual cards in the players hand
            printf("\nYour hand consists of:\n");
            display_hand (handsize, hand);
            // call the display_hand function to display the individual cards in the dealers hand
            printf("Dealer hand consists of:\n");
            display_hand (handsize, dealer);
        }

        // call the findScore function for both the user and the computer
        p = findScore (handsize, hand);
        d = findScore (handsize, dealer);

        // show the value of the user and computers hands
        printf("\nThe value of your hand is %i\n", p);
        printf("\nThe value of the dealers hand is %i\n", d);

        // if statements that keep track of wins, losses and ties
        if (p > d)
            win++;
        if (p == d)
            tie++;
        if (p < d)
            lose++;

        // show number of times player has won, lost, tied.  Then ask to play again
        printf("You have won %i times, tied %i times, and lost %i times\n", win, tie, lose);
        printf("\nWould you like to play again?\n");
        fflush(stdin);      // flush the input buffer to stop false readings
        scanf("%c", &play); // read the user input to determine if they want to play again
    }
    printf("Goodbye");
    return 0;

**我希望这是你想要的

Answer 1

通常首选符号常量(#define 或实际常量)。

例如，当您的代码中充满了值1440，但您使用该数字表示每英寸缇数和每软盘千字节数(在这里非常暴露我的年龄)时，会发生什么情况？ p>

然后你的软盘突然变成了 2.88M。然后，您必须检查所有代码，查找1440，并确定它是否意味着缇或千字节版本，并更改​​相关版本。因此，您不仅必须在多个地方进行更改(这已经够糟糕了)，您可能还必须弄清楚是否要在每个地方进行更改。

如果你这样做:

#define TWIPS_PER_INCH 1440
#define KB_PER_FLOPPY  1440

然后在代码中添加符号名称，您就可以只更改一行行，而无需太多思考或分析。

<小时/>

有一个学派认为，除了零或一(也可能是负数)之外的任何数字都应该有某种符号常数。只要确保您没有犯以下错误即可:

#define FOURTEEN_HUNDRED_AND_FORTY 1440

就像我的一个手下曾经尝试过的那样。我在试图解释为什么那是一个坏主意时获得了无尽的乐趣:-)

<小时/>

至于您的错误，当然可以声明一个带有预处理器常量的数组，如下所示:

#include <stdio.h>
#include <string.h>

#define VAR 42
int main (void) {
    char xyzzy[VAR];
    strcpy (xyzzy, "pax is awesome");
    puts (xyzzy);
    return 0;
}

但是，请考虑代码中的以下几行:

#define size 52
void shuffle_deck (int size, int deck[]);
void display_hand (int size, int hand[]);
int popCard (int *size, int deck[]);
int findScore (int size, int hand[]);
hand[c] = popCard (&size, deck);
// and possibly many others.

因为预处理是在编译过程早期完成的文本替换，所以第一行后面的那些行将变成:

void shuffle_deck (int 52, int deck[]);
void display_hand (int 52, int hand[]);
int popCard (int *52, int deck[]);
int findScore (int 52, int hand[]);
hand[c] = popCard (&52, deck);

它们会导致各种各样的问题，其中52在函数原型(prototype)中不是一个有效的变量名，并且你不能在C中获取整数文字的地址，因为它< em>没有地址。

为了解决这个问题，您将初始大小定义为常量:

#define INIT_SZ 52

并使用它来设置变量 大小的初始值，您可以稍后更改该值，例如:

void doSomethingThatChangesSize (int *pSize) {
    (*pSize) += 42;
}

int size = INIT_SZ; // this is the only way you use INIT_SZ
:
doSomethingThatChanges (&size);