scanf放在循环判断句里面或外面结果不一样

Question

scanf放在循环判断句里面或者外面。运行结果不一样

{ 
    int b;
    while (scanf("%d", &b)!= 5)
    {
        if (5 > b)
            cout << "猜小了" << endl;
        else
            cout << "猜大了" << endl;
    }
      cout<<("猜对了");
}
 输入5，打印猜大了。

int main()
{ 
    int b;
    scanf("%d", &b);
    while (b!= 5)
    {
        if (5 > b)
            cout << "猜小了" << endl;
        else
            cout << "猜大了" << endl;
    }
      cout<<("猜对了");
}

打印猜对了

Answer 1

while (scanf("%d", &b)!= 5)
这个判断的不是b!=5而是scanf函数返回值!=5
而scanf函数返回值为成功读取的变量的个数