为什么程序如果在 C 中不适用于 char

Question

I am writing a simple quiz in C (using CodeBlocks 13.12)

It compiles, but doesn't work in second question. Whatever I will input, it always give answer ' that's sad '. I can't understand what is wrong. I came to this, where if I comment line 13 ( scanf("%d", &age); ) it's starting works ok for second question. What the problem is?

#include <iostream>
#include <stdio.h>
#include <windows.h>
#include <clocale>


int main()
{

int age;
char S1;

printf("How old is your dog? \n");
scanf("%d", &age);

if (age <= 7)
    {
        printf(" very young. the end \n");
        return 0;
    }
else
    {
        printf("old dog. \n \n");
    }

//question2

printf("Do you like dogs? y/n \n");
scanf("%c%c", &S1);

if (S1 == 'y')
    {
         printf("hey, that's nice \n");
    }
else
    {
        printf(" that's sad :( . \n");
        return 0;
    }
 return 0;
}

Answer 1

You cause undefined behavior by

scanf("%c%c", &S1);

scanf reads two char s, one stored in S1 , one stored in some location on the stack because scanf expects a second char* to be supplied.

If your intention is to ignore the newline following the actual character, write

scanf("%c%*c", &S1);

Answer 2

Change the second scanf() to

scanf(" %c", &S1);

This would escape the left out newline character \\n in the input buffer.

Plus, you are reading one char in this. So you need only one %c

Answer 3

scanf("%c", &S1);

是输入一个字符的正确方法，