Question

问题我输入y作为选项，它会在再次提示我之前打印两次文本，因为它应该只打印一次。

正确的输出（我应该得到但未得到的）：

Do you order FISH (Y/N)? y
Fish choice (K- Haddock, T- Halibut)

Do you order FISH (Y/N)? y
Fish choice (K- Haddock, T- Halibut)

Do you order FISH (Y/N)? n

Do you order CHIPS (Y/N)? n

Do you order DRINKS (Y/N)? y
Drinks choice (S- Softdrink, C- Coffee, T- Tea)

Do you order DRINKS (Y/N)? n

错误输出（我得到的输出）

Do you order FISH (Y/N)? y
Fish choice (K- Haddock, T- Halibut)
Do you order FISH (Y/N)? Fish choice (K- Haddock, T- Halibut)
Do you order FISH (Y/N)? y
Fish choice (K- Haddock, T- Halibut)
Do you order FISH (Y/N)? Fish choice (K- Haddock, T- Halibut)
Do you order FISH (Y/N)? n
Do you order CHIPS (Y/N)? Chips choice (C- Cut, R- Ring)
Do you order CHIPS (Y/N)? n
Do you order DRINKS (Y/N)? Drinks choice (S- Softdrink, C- Coffee, T- Tea):
Do you order DRINKS (Y/N)? n

RAW SOURCE （如果您想自己编译并查看最新信息）：http://pastebin.com/raw.php?i=mZ1jVrF0

来源

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

int main() {

    char fishYesNo, chipsYesNo, drinksYesNo;
    char *typeOfFood;

    do {
        typeOfFood = "fish";
        printf("Do you order FISH (Y/N)? ");
        scanf("%c", &fishYesNo);
        if (fishYesNo != 'n') {
            printf("Fish choice (K- Haddock, T- Halibut) \n");

        }
        else if (fishYesNo == 'n') {
            typeOfFood = "chips";
        }

    } while ((strcmp(typeOfFood, "fish")) == 0);

    do {
    typeOfFood = "chips";
        printf("Do you order CHIPS (Y/N)? ");
        scanf("%c", &chipsYesNo);
        if (chipsYesNo != 'n') {
            printf("Chips choice (C- Cut, R- Ring) \n");
        }
        else if (chipsYesNo == 'n') {
            typeOfFood = "drinks";
        }

    } while ((strcmp(typeOfFood, "chips")) == 0);

    do {
    typeOfFood = "drinks";
        printf("Do you order DRINKS (Y/N)? ");
        scanf("%c", &drinksYesNo);
        if (drinksYesNo != 'n') {
            printf("Drinks choice (S- Softdrink, C- Coffee, T- Tea):\n");
        }
        else if (drinksYesNo == 'n') {
            typeOfFood = "fish";
        }

    } while ((strcmp(typeOfFood, "drinks")) == 0);

}

Answer 1

这是C中一个众所周知的概念错误。comp.lang.c FAQ（我建议你阅读）有很多关于这个和其他陷阱的信息。

解释代码中发生了什么（comp.lang.c FAQ list · Question 12.18b）：

您希望scanf %c读取单个字符，并且尝试了，但是当你试图在它的其余部分之前输入那个单个字符时输入系统会接受它，你也必须点击RETURN键。 scanf只读取一个字符，但额外的换行符仍然存在坐在某处的输入缓冲区中，它就是额外的换行符（似乎代表一个幻影空白行）被收到了你以后的输入电话。

如何处理这一问题，请查看scanf的问题（comp.lang.c FAQ list · Question 12.20）：

几乎不可能优雅地处理所有这些潜力使用scanf时遇到的问题;它更容易阅读整行（有 fgets等等，然后使用sscanf或其他方式解释它们其他技术。

在C中重复循环

1 个答案: