c - 如何限制只能输入一个字母？

Question

我意识到，如果输入是以“y”或“n”开头的单词，它将跳出循环。如何限制循环，使其继续循环，除非输入是单个字符？

do
{
    printf("Do you want to try again? (Y/N): ");
    fflush(stdin);                              
    scanf("%c", &repeat);
    repeat = toupper(repeat);
    if (repeat != 'Y' && repeat != 'N')         
        printf("Invalid answer. Please enter 'Y' or 'N'.\n\n");

} while (repeat != 'N' && repeat != 'Y'); 

Answer 1

像这样:

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

int main(void){
    char repeat[3] = {0};//3 : one character + one character + NUL
    do{
        printf("Do you want to try again? (Y/N): ");fflush(stdout);
        if(EOF==scanf("%2s", repeat)){ *repeat = 'N'; break; }
        *repeat = toupper(*repeat);
        if (repeat[1] || *repeat != 'Y' && *repeat != 'N'){//repeat[1] != '\0'..     
            printf("Invalid answer. Please enter 'Y' or 'N'.\n\n");
            scanf("%*[^\n]");scanf("%*c");//clear upto newline
            *repeat = 0;
        }
    } while (*repeat != 'N' && *repeat != 'Y'); 
    puts("Bye!");//try agein or see ya, bye
    return 0;
}