getchar在开关情况下不工作（c）

使用一个非常简单的计算器程序，提示用户执行一个操作，然后提示输入两个要执行此操作的整数。程序应该在这些操作后循环，除非用户输入字符“q”，此时程序应该退出

#include <stdio.h>

int main (void)
    {
        char c;
        int number[2], num1, num2, result;
        double num1d, num2d, resultd;
        int done=1;

        while(done)
        {
        printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
        c = getchar();
        printf("\tplease enter a number \n");
        scanf("%d",&number[0]);
        printf("\tplease enter another number \n");
        scanf("%d",&number[1]);
        num1 = number[0];
        num2 = number[1];

        switch(c)
            {
            case('-'):
            result = num1-num2;
            printf("\nThe first number you entered subtracted by the second number is %d.\n", result);
            break;

            case('+'):
            result = num1+num2;
            printf("The first number you entered added to the second number is %d.\n", result);
            break;

            case('*'):
            result = num1*num2;
            printf("The first number you entered multiplied with the second number is %d.\n", result);
            break;

            case('/'):
            num1d = (double) num1;
            num2d = (double) num2;
            resultd = num1d/num2d;
            printf("The first number you entered divided by the second number is %g.\n", resultd);;
            break;

            case('q'):
            printf(" Now Exiting...\n");
            done=0;
            break;

            default:
            puts("Invalid key pressed. Press q to exit");
            break;
            }
        }

        return 0;
    }

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

总共

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

---

getchar！='时清除输入缓冲区的标准方法\n′；不能解决这个问题。此文本显示不正确的两次中有一次，用户仍然可以使用程序，就好像指令按应有的方式显示一样，因此用户可以键入一个操作，例如+、回车，然后键入某个整数和回车，并且每隔一次，程序将从该点正确执行，但程序将按下无效键。无论输入如何，按q退出

您不应该将字符与更高级的输入函数（如scanf）混合使用。最好也使用scanf输入命令字符，但当然，在命令之后必须按enter键。我相信这是你问题的根源

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

另一方面，请注意getchar，不管它的名称如何，都返回int，而不是char。这是因为它可以返回EOF，EOF是一个特殊常量，其值不同于所有字符的值

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

此外，您应该始终检查I/O函数（如scanf）的返回值，如果输入与模式字符串不匹配，它们可能会失败

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

---

作为调试提示，您当然可以在解释c之前打印c的值，以便更容易地查看和理解程序的流程。

您不应该将字符与更高级的输入函数（如scanf）混用。最好也使用scanf输入命令字符，但当然，在命令之后必须按enter键。我相信这是你问题的根源

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

另一方面，请注意getchar，不管它的名称如何，都返回int，而不是char。这是因为它可以返回EOF，EOF是一个特殊常量，其值不同于所有字符的值

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

此外，您应该始终检查I/O函数（如scanf）的返回值，如果输入与模式字符串不匹配，它们可能会失败

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

---

作为调试提示，您当然可以在解释c之前打印c的值，以便更容易地查看和理解程序的流程。

您的getchar应该返回int。原因如下

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

getchar reads characters from the program's standard input 
and returns an int value suitable for storing into a char. 
The int value is for one reason only: not only does getchar 
return all possible character values, but it also returns an 
extra value to indicate that end-of-input has been seen. 
The range of a char might not be enough to hold this extra value, 
so the int has to be used.

---

因此，基本上您需要在代码中将char c更改为int c，getchar应该返回int

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

getchar reads characters from the program's standard input 
and returns an int value suitable for storing into a char. 
The int value is for one reason only: not only does getchar 
return all possible character values, but it also returns an 
extra value to indicate that end-of-input has been seen. 
The range of a char might not be enough to hold this extra value, 
so the int has to be used.

---

所以基本上你需要在你的代码中将char c改为int c，我猜第一次可以，但下一次不行。这是因为scanf调用将换行符留在输入缓冲区中，因此下次在循环中调用getchar时，它将返回换行符。在scanf调用中的格式后添加空格

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

它将丢弃缓冲区中剩余的空白

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

---

使用调试器逐步完成代码并检查要验证的变量。

我猜它第一次起作用，但下次不起作用。这是因为scanf调用将换行符留在输入缓冲区中，因此下次在循环中调用getchar时，它将返回换行符。在scanf调用中的格式后添加空格

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

它将丢弃缓冲区中剩余的空白

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

---

使用调试器逐步完成代码并检查变量以进行验证。

这里的其他人都说的是真的，getchar返回int，但这不是您的问题

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

问题是getchar在使用后会留下一个换行符。如果要使用getchar，则必须始终在之后使用换行符。这是一个简单的解决方案：

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

   printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
    c = getchar();
    getchar();     //<-- here we do an extra getchar for the \n
    printf("\tplease enter a number \n");
    scanf("%d",&number[0]);
    printf("\tplease enter another number \n");
    scanf("%d",&number[1]);

---

getchar将只获取其中的第一个，然后当再次调用getchar时，它不会等待您的输入，它将只获取“\n”并继续扫描。这里的其他人都说是真的，getchar返回一个int，但这不是您的问题

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

问题是getchar在使用后会留下一个换行符。如果要使用getchar，则必须始终在之后使用换行符。这是一个简单的解决方案：

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

   printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
    c = getchar();
    getchar();     //<-- here we do an extra getchar for the \n
    printf("\tplease enter a number \n");
    scanf("%d",&number[0]);
    printf("\tplease enter another number \n");
    scanf("%d",&number[1]);

---

getchar将只获取其中的第一个，然后当再次调用getchar时，它将不会等待您的输入，它将只获取“\n”并转到scanf

我听说getchar返回整数这一事实，这让我非常惊讶。然而，你知道为什么这可以解释这种奇怪的行为吗？@Duncan-不知道。从getchar中获取一个char的事实只意味着输入可能会溢出，即int可以容纳多个char。你的问题是保留换行符，看看我的答案。我听说getchar返回整数，这让我很惊讶。然而，你知道为什么这可以解释这种奇怪的行为吗？@Duncan-不知道。这个

printf("\t What sort of operation would you like to perform? \n \t Type + - * / accordingly. \n");
printf("\tplease enter a number \n");

---

从getchar中获取一个char的事实只意味着输入可能会溢出，即int可以容纳多个char。您的问题是保留换行符请参阅我的答案。虽然getchar返回int是真的，但该建议并不能解决问题。虽然getchar返回int是真的，但该建议并不能解决问题。谢谢兄弟，这很有用：谢谢兄弟，这很有用：