递增整数和初始化位置有奇怪的效果？

Question

我用 C 编写了以下 'Hangman game' 程序（写得又快又脏所以不要介意代码太多）：

#include <stdio.h>

int main() {
    char word[] = "cat";
    int amountGuessesAllowed = 5;
    size_t size = sizeof(word)-1; // -1 to exclude the '[=10=]'

    char guessedWord[size];
    for (int i=0; i<size; i++){
        guessedWord[i] = '_';
    }

    int lettersGuessed = 0;
    int totalTimesGuessed = 0;
    char c;

    printf("%s\n", guessedWord);
    printf("Guess %d - Enter a character: ", totalTimesGuessed+1);
    scanf("%s", &c);

    while (totalTimesGuessed < amountGuessesAllowed) {
        for(int i=0; i<size; i++){
            if (word[i] == c && guessedWord[i] == '_'){
                printf("It matches character at index %d!\n", i);
                guessedWord[i] = c;
                lettersGuessed++;
                printf("letters guessed: %d\n", lettersGuessed);
            }
        }
        totalTimesGuessed++;
        if (lettersGuessed == size) {
            printf("You win!");
            return 0;
        } else if (totalTimesGuessed == amountGuessesAllowed) {
            printf("You lose!");
            return 0;
        } else {
            printf("%s\n", guessedWord);
            printf("Guess %d - Enter a character: ", totalTimesGuessed+1);
            scanf("%s", &c);
        }
    }
}

问题似乎与 lettersGuessed、totalTimesGuessed 和 c[=41= 这三个初始化行有关].

如果您执行该程序并输入几个字母，您会注意到由于某种原因，totalTimesGuessed-值始终显示为 2，它似乎不再递增。 lettersGuessed 变量似乎没有任何问题。

___ Guess 1 - Enter a character: b ___ Guess 2 - Enter a character: c It matches character at index 0! letters guessed: 1 c__ Guess 2 - Enter a character: j c__ Guess 2 - Enter a character:

现在，如果您要交换 lettersGuessed 和 totalTimesGuessed 的顺序，那么 lettersGuessed 变量就会出现问题（仍然是 1）！

___ Guess 1 - Enter a character: c It matches character at index 0! letters guessed: 1 c__ Guess 2 - Enter a character: a It matches character at index 1! letters guessed: 1 ca_ Guess 3 - Enter a character:

最后，如果我将 char c; 行放在两个整数之前：

char c; int lettersGuessed = 0; int totalTimesGuessed = 0;

然后一切正常！

___ Guess 1 - Enter a character: c It matches character at index 0! letters guessed: 1 c__ Guess 2 - Enter a character: a It matches character at index 1! letters guessed: 2 ca_ Guess 3 - Enter a character:

我已经在 Xcode 中用 gcc 测试了这个。

这必须有一个合乎逻辑的解释吗？我渴望开悟！

Answer 1

您在

中造成了未定义的行为

scanf("%s", &c);

因为 "%s" 说明符向目标添加了一个终止 nul 字节，它是一个 char.

你可以试试

if (scanf(" %c", &c) != 1)
    handleErrorPlease();

"%c" 之前的 space 是有意的，它会吃掉之前调用 scanf.

留下的任何白色 space 字符

当发生未定义的行为时，实际发生的情况取决于程序在加载内存时的布局，因此更改已定义变量的顺序会导致行为不同。

递增整数和初始化位置有奇怪的效果？

Incrementing an integer and initialisation placement having a weird effect?

c

int

loops