scanf（“％C”，& opt）和scanf（“％C”，& opt）之间的差异 [英] Difference between scanf("%C", &opt) and scanf(" %C", &opt)

问题描述

我在IDE TurboC3中执行我的c语言程序。

非工作代码如下

I am executing my c language program in IDE TurboC3.
Non working code is as follows

#include<stdio.h>
#include<conio.h>
void main()
    {
    int i, j, t;
    char opt;
    clrscr();
    printf("Enter two values" );
    scanf("%d", &i);
    scanf("%d", &j);
    printf("\n\n press + for sum\n");
    printf("press * for mult\n");
    printf("print - for subtract\n\n");
    scanf("%c", &opt); // code that is creating problem //
    switch(opt)
        {
        case '+':
            {t=i+j;
            printf("\nsum =%d", t);
            }
            break;
        case '*':
            {t=i*j;
            printf("\nproduct =%d", t);
            }
            break;
        case '-':
            {t=i-j;
            printf("\ndifference =%d", t);
            }
        break;
        default:
            printf("\ninvalid choice");
        }
    getch();
    }

代码块已更正，缩进添加 - OriginalGriff [/ edit]



我尝试了什么：



帮助我执行代码的更正如下

[edit]Code block corrected, indentation added - OriginalGriff[/edit]

What I have tried:

The correction that helped me execute the code is as follows

scanf(" %c", &opt); // code without problem //

即我在和％c之间插入了一个空格和代码工作。



请帮我理解其中的区别。

i.e. i have inserted a space between " and %c and the code worked.

Please help me understand the difference.

推荐答案

不同之处在于scanf按字面意思使用格式字符串：对空格的需要意味着您的输入不是+，而是在它之前有空格。％c是一个scanf特殊代码：它根本不会跳过空格字符（不像％d那样）。所以当你的用户输入这两个值时，终结符可能留在缓冲区中并作为第一个字符返回而不是用户键入的'*'或'+'。



说实话，你可能最好使用getch和循环，特定的退出字符，而不是读取一个字符并停止。

个人？我会在单独的行中提示每个号码，将其读作char数组，并将其扫描成一个数字 - 这样我就可以应对用户输入错误而不是像你的代码那样崩溃。然后我会为运营商使用getch。

The difference is that scanf uses the format string literally: the need for a space implies that your input is not '+' but has whitespace before it. "%c" is a scanf "special" code: it does not skip whitespace characters at all (unlike "%d" which does). So when your user entered the two values, the terminator was probably "left in the buffer" and returned as the first character instead of the '*' or '+' that the user typed.

To be honest, you'd probably be better off using getch and a loop, with a specific "exit" character instead of reading one char and stopping.
Personally? I'd prompt for each number on a separate line, read it as a char array, and scan that into a number - that way I could cope with user input errors instead of crashing as your code will. Then I'd use getch for the operator.

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