递归下降的语法分析器

希望可以帮我南航金城的学弟学妹们,嘿嘿

#include<iostream>
#include<string>

using namespace std;
string str;//句子
int flag = 0;//0标记合法,1标记非法
int i = 0;
void E();
void F();
void E1();
void T1();
void T();
void E()
{
T();
E1();
}

void E1()
{
if(str[i] == '+' )
{
cout<<"E->TE1"<<endl;
cout<<"E1->+TE1|ε"<<endl;

i++;
T();
E1();


}


}

void T()
{
F();
T1();
}

void T1()
{
if(str[i] == '*' )
{
cout<<"E->TE1"<<endl;
cout<<"T->FT1 "<<endl;
cout<<"T1->*FT1|ε"<<endl;

i++;
F();
T1();
}
}

void F()
{
if(str[i] == 'i')
{
i++;
}
else
{cout<<"F->(E)|i"<<endl;
if(str[i] == '(')
{
i++;
E();
if(str[i] == ')')
{
i++;
}
else
{
flag = 1;
cout << "error" << flag << endl;
}
}
else
{
flag = 2;
cout << "error" << flag << endl;
}
}
}

int main()
{
cout << "请输入字符串(以'#'结束)..." << endl;
cin >> str;
E();
if(str[i] == '#'
&& flag == 0)
cout << "为合法符号串!" << endl;
else
cout << "为非法的符号串!" << endl;
return 0;
}