设计，编制并调试一个词法分析程序

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define LEN sizeof(struct Node)

struct Node
{
char data;
struct Node *next;
};
struct Node *head,*p;
char ch;
char *key[7]={"main","inf","char","if","else","for","while"};
char token[20];

void getch()
{
ch =p->data;
p=p->next;
}

void output(struct Node *head)
{
if(!head)
{
printf("Something wrong with head node!");
exit(1);
}
p=head->next;

while(p->next!=NULL)
{
printf("%c",p->data);
p=p->next;
}
printf("\n");
}

void getbc()
{
while(ch==' ')
getch();
}

void concat()
{
unsigned int i;
i=strlen(token);
token[i]=ch;
token[i+1]='\0';
}

int letter(char ch)
{
return isdigit((int)ch);
}

int digit(char ch)
{
return isdigit((int)ch);