[Error] qualified-id in declaration before '(' token [Error] expected '}' at end

#include <fstream>
#include <iostream>
#include <cstdlib>
#include <string>
using namespace std;
int N;
class student
{
public:
void addstudent ();
void deletestudent ();
void findstudent ();
void changestudent ();
void writetofile ();
void readfromfile ();
void sumstudent ();
private:
long id;
string name;
string sex;
string place;
long telnum;
string mail;

};
void student::addstudent()
{
int i=0,t;
cout<<"请输入要添加的人数"<<endl;
cin>>t;
N=N+t;
student stu[N];
for(;i<N;i++)
{
cout<<"请输入第"<<i+1<<"个学生学号、姓名、性别、工作单位、电话号码、E-mail地址"<<endl;
cin>>stu[i].id>>stu[i].name>>stu[i].sex>>stu[i].place>>stu[i].telnum>>stu[i].mail;
}
}
void student::deletestudent()
{
string Name;
int i=0,a=-1;
cout<<"请输入要删除的学生名字"<<endl;
cin>>Name;
student stu[N];
for(;i<N;i++)
{
if(Name==stu[i].name)
{
a=i;
break;
}
if(a==-1)
{
cout<<"找不到该学生"<<endl;
}
else
{
for(i=a;i<N-1;i++)
{
stu[i]=stu[i+1];
}
cout<<"删除成功"<<endl;
}
}
void student::findstudent()
{
string Name;
student stu[N];
cout<<"请输入要查询的学生姓名"<<endl;
cin>>Name;
int i=0;
for(;i<N;i++)
{
if(Name==stu[i].name)
{
a=i;
break;
}
if(a==-1)
{
cout<<"找不到该学生"<<endl;
}
else
{
cout<<stu[a].id<<stu[a].name<<stu[a].sex<<stu[a].place<<stu[a].telnum<<stu[a].mail;
}
}
void student::changestudent()
{
int i=0;
string Name;
student stu[N];
cout<<"请输入要修改的学生姓名"<<endl;
cin>>Name;
for(;i<N;i++)
{
if(Name==stu[i].name)
{
a=i;
break;
}
if(a==-1)
{
printf("找不到该学生\n");
}
else
{
cout<<stu[a].id<<stu[a].name<<stu[a].sex<<stu[a].place<<stu[a].telnum<<stu[a].mail;
}
}
void student::writetofile()
{
}
void student::readfromfile()
{
}
void student::sumstudent()
{
}
void menu()
{
student stu;
cout<<"欢迎使用同学通讯录"<<endl;
cout<<"请选择功能"<<endl;
cout<<"1.显示所有学生信息"<<endl;
cout<<"2.添加学生信息"<<endl;
cout<<"3.删除学生信息"<<endl;
cout<<"4.查询学生信息"<<endl;
cout<<"5.修改学生信息"<<endl;
cout<<"6.显示男女同学人数和总人数"<<endl;
cout<<"7.读取文件"<<endl;
int a;
cin>>a;
while(1)
{
switch(a)
{
case 1:
stu.readfromfile();
break;
case 2:
stu.addstudent();
break;
case 3:
stu.deletestudent();
break;
case 4:
stu.findstudent();
break;
case 5:
stu.changestudent();
break;
case 6:
stu.sumstudent();
break;
case 7:
stu.readfromfile();
break;
}
}
}
int main()
{
menu();
return 0;
}