Dev C++下C语言MCQ测试程序输入异常问题求助

问题描述 #

编程新手使用Dev C++编写C语言选择题测试程序时遇到输入异常：第一个题目可正常接收输入，第二个题目无法获取输入直接判定错误。

程序代码 #

#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<math.h>
#include <stdlib.h>
#include<windows.h>
#include <time.h>

void main()
{
    printf("Welcome to MCQs Test.\nPhysics CH # 1\nExercise MCQs......\nChoose the correct answer.\n\n");
    
    char ans;
    int true = 0, false = 0, count = 0;
    printf("1) Which of the following is an example of Simple Harmonic Motion?\n\n");
    printf("A. Motion of a simple pendulum\nB. The motion of ceiling fan\nC. The spinning of the Earth around its axis\nD. A bouncing ball on a floor\n\n");
    printf("Select your answer (a, b, c, d): ");
    scanf("%c", &ans);
    if(ans == 'a'){
        printf("\nCorrect ^_^\n\n");
        true++;
    } else if(ans != 'a'){
        printf("\nOops! Your answer is Wrong.\nThe Correct answer is: 'A. Motion of a simple pendulum'  \nBetter luck Next time....\n\n");
        false++;
    }
    count++;
    printf("Press any key to continue...\n\n");
    getch();
    
    printf("2) If the mass of the bob of a pendulum is increased by a factor of 3, the period of the pendulum`s motion will\n\n");
    printf("A. be increased by a factor of 2\nB. remain the same\nC. be decreased by a factor of 2\nD. be decreased by a factor of 4\n\n");
    printf("Select your answer (a, b, c, d): ");
    scanf("%c", &ans);
    if(ans == 'b'){
        printf("\nCorrect ^_^\n\n");
        true++;
    } else if(ans != 'b'){
        printf("\nOops! Your answer is Wrong.\nThe Correct answer is: 'B. remain the same'  \nBetter luck Next time....\n\n");
        false++;
    }
    count++;
    printf("Press any key to continue...\n\n");
    getch();
    
    printf("%d of your answers is/are correct while %d is/are incorrect out of %d Questions\n", true, false, count);
    printf("Press any key to continue...\n\n");
    
    getch();
}

程序运行输出 #

Welcome to MCQs Test.
Physics CH # 1
Exercise MCQs......
Choose the correct answer.

1) Which of the following is an example of Simple Harmonic Motion?

A. Motion of a simple pendulum
B. The motion of ceiling fan
C. The spinning of the Earth around its axis
D. A bouncing ball on a floor

Select your answer (a, b, c, d): a

Correct ^_^

Press any key to continue...

2) If the mass of the bob of a pendulum is increased by a factor of 3, the period of the pendulum`s motion will

A. be increased by a factor of 2
B. remain the same
C. be decreased by a factor of 2
D. be decreased by a factor of 4

Select your answer (a, b, c, d): 

实际异常表现 #

Oops! Your answer is Wrong.
The Correct answer is: 'B. remain the same'
Better luck Next time....

Press any key to continue...

1 of your answers is/are correct while 1 is/are incorrect out of 2 Questions
Press any key to continue...

问题原因与解决方法 #

原因分析 #

第一个题目输入完成后，按下的**回车键（换行符\n）**会残留在输入缓冲区中。当第二个scanf("%c", &ans);执行时，它会直接读取这个换行符，而非等待用户输入新字符，导致程序直接判定答案错误。

解决方法 #

有两种简单的修复方式：

方法1：在scanf格式字符串前添加空格

将所有scanf("%c", &ans);修改为scanf(" %c", &ans);。这里的空格会跳过输入缓冲区中的所有空白字符（包括换行符、空格、制表符等），确保scanf读取到的是用户输入的有效字符。

修改后的关键代码片段：

printf("Select your answer (a, b, c, d): ");
scanf(" %c", &ans); // 格式字符串前添加空格

方法2：手动丢弃缓冲区中的换行符

在第一个题目处理完成后的getch();之后，添加getchar();来读取并丢弃缓冲区中残留的换行符：

printf("Press any key to continue...\n\n");
getch();
getchar(); // 丢弃缓冲区中的换行符

额外建议 #

• 标准C中main函数的返回类型应为int，而非void main()，建议修改为int main()并在函数末尾添加return 0;。
• true和false是C99及以后标准的关键字，避免将它们用作变量名，可改为correct、incorrect等名称，避免潜在编译问题。

内容的提问来源于stack exchange，提问作者Huzaifa Tahir