未声明过的标识符

class CDog
{
public:
    unsigned int m_Weight;
    unsigned int m_Age;
    CDog();
    ~CDog();
};
CDog::CDog()
{
    m_Age=1;
    m_Weight=2;
    printf("construct instance\n");
}
CDog::~CDog()
{

}
int main(int argc, char* argv[])
{
    CDog mydog;
    printf("%/d",mydog.m_Age);
    return 0;
}



为什么显示printf是未声明过的标识符
怎么改?