c - 字母猜谜游戏奇怪的输出

Question

这是我的代码:

#define _CRT_SECURE_NO_DEPRECATE
#include <stdio.h> 
#define MAX_GUESSES 4
int PlayGame(char guess);
int WinOrLose(char userguess, char solution);
int main()
{
        FILE* infile;
    char correctlet;
    int games,
        igame,
        result;
    infile = fopen("inputLet.txt", "r");
    printf ("Welcome to the letter guessing game!\n");
    printf ("Your job is to guess a random letter.\n");
    printf("You can guess each letter a maximum of 4 times,\n");
    printf ("and you will get a hint after every guess.\n");
    printf ("LET'S DO THIS!\n\n>");
    printf ("\nHow many games would you like to play (1-3)?\n>");
    scanf ("%d",&games);
    for(igame=0;igame<games;igame++)
    {
        fscanf(infile," %c",&correctlet);
        printf("This is game %d\n", igame+1);
        result = PlayGame (correctlet);
        if (result == 0)
        {
            printf ("\nCongratulations, you guessed the right letter!\n");
        }
        else
        {
            printf ("\nUnfortunately, you did not guess the right letter. Better luck next time!\n");
    }
    }
    return 0;
}
int PlayGame(char solution)
{
    int guessnumber,
        result;
    char userguess;
    guessnumber = 0;
    while(guessnumber < MAX_GUESSES)
    {
        printf("Please enter your guess\n>");
        scanf("%c", &userguess);
        if (sizeof userguess == 0)
        {
            continue;
        }
        else if (sizeof userguess >=1)
    {
        printf ("Your guess was %c\n",userguess);
        result = WinOrLose (userguess, solution);
        if (result == 0)
        {
            return 0;
            break;
        }
        else if (result == 1)
        {
            if (solution < userguess)
            {
                printf("The correct letter comes before %c alphabetically\n", userguess);
            }
            else if (solution > userguess)
            {
                printf("The correct letter comes after %c alphabetically\n", userguess);
            }
        guessnumber ++;
        }
    }
}
}
int WinOrLose (char userguess, char solution)
{
    if(solution==userguess)
    {
        return 0;
    }
    else if (solution != userguess)
{
    return 1;
}
}

输出询问游戏的数量，然后它输出请输入您的猜测您的猜测是(空白)正确的字母在后面(空白)请输入您的猜测然后它允许用户输入。那么为什么它在不要求用户输入的情况下进行一次 PlayGame 迭代呢？我已经尝试了所有我能想到的方法，但无法解决问题。如果有帮助，我正在编译 VC++ 2010。提前致谢!

Answer 1

简单的答案是刷新缓冲区。

stdin 缓冲区，从键盘(或管道)获取指令并将其提交给程序的缓冲区偶尔会在其中“卡住”一些字符。从未完全提交的垃圾字符、额外的返回等会导致 scanf() 认为它已到达正确的终点，但实际上并没有。

fflush(stdin);

函数 fflush “刷新”缓冲区。这样做的效果是消耗缓冲区中的数据，直到接收到的数据是字符“\0”(NULL)。这意味着它已到达缓冲区中当前的最后一个数据。

在调用 scanf() 之前调用它意味着当调用 scanf() 时，您有理由知道程序将阻塞 scanf() 直到您提交，而不仅仅是消耗缓冲区中的一些垃圾。