left operand must be l-value(在线等待)

left operand must be l-value(在线等待)
#include
void main()
{
struct student
{
long int num;
char name[30];
char sex;
char addr[30];
}a;
a.num=2;
a.name="Li shuai";
a.sex='F';
a.addr="123 qinghe Road";
printf("No.%ldnname:%snsex:%cnaddress:% sn",a.num,a.name,a.sex,a.addr);
printf("%on",&a);
}
提示 a.num a.addr是"left operand must be l-value"?
a.num和a.addr是变量,不是常量,怎么会出现这种问题?