C语言答题游戏正确答案判定失败的Bug原因排查

核心问题 #

你的代码里有两个关键错误导致正确答案无法被识别：

1. 无效的scanf调用：scanf("%c");这个语句缺少必要的指针参数，属于未定义行为，会破坏程序内存结构，导致输入的答案值被篡改或读取异常。
2. 输入缓冲区换行符未正确处理：用户输入答案后按回车，输入缓冲区会残留换行符，直接用scanf("%c", &ans)会在后续循环中读取到这个换行符，导致ans的值变成换行符，自然无法匹配正确答案。

修复后的代码 #

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

int main()
{
    char questions[][100] = {
        "\n1. what company was the first to create a foldable phone? ",
        "\n2. what company was the first to create a foldable laptop? ",
        "\n3. what company was the first to create a full electric car? "
    };

    char options[][100] = {
        "\nA. apple, B. oppo, C. samsung, D. motorolla",
        "\nA. Asus, B. MSI, C. Microsoft, D. Gygabyte",
        "\nA. mazda, B. chevrollet, C. toyota, D. Tesla"
    };

    char answers[] = {'C', 'A', 'D'};

    int score = 0;
    char ans;

    for (int i = 0; i < sizeof(questions) / sizeof(questions[0]); i++)
    {
        printf("%s", questions[i]);
        printf("%s", options[i]);

        printf("\n\nwhat is your answer? ");
        // 修改这里：用空格跳过空白字符，确保读取到有效答案
        scanf(" %c", &ans);

        ans = toupper(ans);

        if (ans == answers[i])
        {
            score += 1;
            printf("\nthat's right!");
            printf("\nnext question\n");
        }
        else
        {
            printf("\nwrong!");
            printf("\nnext question\n");
        }
    }

    printf("\n\nthe correct answers are:  ");
    for (int i = 0; i < sizeof(questions) / sizeof(questions[0]); i++)
    {
        printf("%c  ", answers[i]);
    }

    printf("\nyour score is: %d/3", score);
}

修改说明 #

• 删掉了错误的scanf("%c");语句，避免内存破坏。
• 将读取答案的scanf("%c", &ans);改为scanf(" %c", &ans);，格式串开头的空格会让scanf自动跳过所有空白字符（换行、空格、制表符等），保证每次读取到的都是用户输入的答案字符，不会被残留的换行符干扰。

内容的提问来源于stack exchange，提问作者Milad Bannourah