c - 为什么这个c程序打印两次

Question

#include <stdio.h>

int main()
{
        char c = 'A';
        while (c != ',')
        {
                printf("Input a character:");
                scanf("%c", &c);
                if (c >= '0' && c <= '9')
                {
                        printf("%d\n", (int)c);
                }
        }
}

接受第一组输入后，这段代码每次都会打印两次“输入一个字符” - 这是为什么？

Answer 1

因为你按下一个数字加上 Enter，并且 Enter 将在下次调用时被 scanf() 读取

#include <stdio.h>

int main(void) {
  char c = 'A';
  while (c != ',') {
    printf("Input a character:");
    if (scanf("%c", &c) != 1) {
      return 0; // we stop if user don't input anything
    }
    if (c >= '0' && c <= '9') {
      printf("%d\n", (int)c); // by the way did you want (int)(c - '0') ?
    } else {
      printf("enter a number ! you enter %d\n", c);
    }
  }
}