c++ lexical analyzer

The lexical analyzer scans a program to determine whether it is a keyword, identifier, constant, delimiter, or operator. Generally divided into one type and five classics;

Here I use the classic five, this lexical analyzer is written in c++;

/*
Reserved Word | Keyword: 1
Operator | Operator: 2
Delimiter: 3
Identifier: 4
Constant: 5
No Recognition: 6
*/

The main code is:

#include<iostream>
using namespace std;
#define MAX 10
/*
	Reserved Words | Keywords: 1
	operator | operator: 2
	Delimiter: 3
	Identifier: 4
	Constant: 5
	No recognition: 6
*/
char ch = ' ';
char* keyWord[10] = {"void","main","break","include","begin","end","if","else","while","switch"};
char token[20];//Define the acquired character
// Determine if it is a keyword
bool isKey (char * token)
{
	for(int i = 0;i < MAX;i++)
	{
		if(strcmp(token,keyWord[i]) == 0)
			return true;
	}
	return false;
}
// Determine if it is a letter
bool isLetter(char letter)
{
	if((letter >= 'a' && letter <= 'z')||(letter >= 'A' && letter <= 'Z'))
		return true;
	else
		return false;
}
// Determine if it is a number
bool isDigit(char digit)
{
	if(digit >= '0' && digit <= '9')
		return true;
	else
		return false;
}
//lexical analysis
void analyze(FILE *fpin)
{
	
	while((ch = fgetc(fpin)) != EOF){
		if(ch == ' '||ch == '\t'||ch == '\n'){}
		else if(isLetter(ch)){
			char token[20]={'\0'};
			int i=0;
			while(isLetter(ch)||isDigit(ch)){	
				token[i] = ch;
				i++;
				ch = fgetc(fpin);
			}
			// rollback a pointer
			fseek(fpin,-1L,SEEK_CUR);
			if(isKey(token)){
				//keyword
				cout<<token<<"\t1"<<"\t关键字"<<endl;
			}
			else{
				//identifier
				cout<<token<<"\t4"<<"\t标识符"<<endl;		
			}
		}
		else if(isDigit(ch)||(ch == '.'))
		{
			int i=0;
			char token[20]={'\0'};
			while(isDigit(ch)||(ch == '.'&&isDigit(fgetc(fpin))))
			{
				if(ch == '.')fseek(fpin,-1L,SEEK_CUR);
				token[i] = ch;
				i++;
				ch = fgetc(fpin);
			}
			fseek(fpin,-1L,SEEK_CUR);
			// is an unsigned constant
			cout<<token<<"\t5"<<"\t常数"<<endl;
		}
		else switch(ch){
			// operator
			case '+':{
						ch = fgetc(fpin);
						if(ch == '+')cout<<"++"<<"\t2"<<"\t运算符"<<endl;
						else {
							cout<<"+"<<"\t2"<<"\t运算符"<<endl;
							fseek(fpin,-1L,SEEK_CUR);
						}
					 }break;
			case '-':{
						ch = fgetc(fpin);
						if(ch == '-')cout<<"--"<<"\t2"<<"\t运算符"<<endl;
						else {
							cout<<"-"<<"\t2"<<"\t运算符"<<endl;
							fseek(fpin,-1L,SEEK_CUR);
						}
					 }break;
			case '*':cout<<ch<<"\t2"<<"\t运算符"<<endl;break;
			case '/':cout<<ch<<"\t2"<<"\t运算符"<<endl;break;
			// delimiter
			case '(':cout<<ch<<"\t3"<<"\t分界符"<<endl;break;
			case ')':cout<<ch<<"\t3"<<"\t分界符"<<endl;break;
			case '[':cout<<ch<<"\t3"<<"\t分界符"<<endl;break;
			case ']':cout<<ch<<"\t3"<<"\t分界符"<<endl;break;
			case ';':cout<<ch<<"\t3"<<"\t分界符"<<endl;break;
			case '{':cout<<ch<<"\t3"<<"\t分界符"<<endl;break;
			case '}':cout<<ch<<"\t3"<<"\t分界符"<<endl;break;
			// operator
			case '=':{
						ch = fgetc(fpin);
						if(ch == '=')cout<<"=="<<"\t2"<<"\t运算符"<<endl;
						else {
							cout<<"="<<"\t2"<<"\t运算符"<<endl;
							fseek(fpin,-1L,SEEK_CUR);
						}
					 }break;
			case ':':{
						ch = fgetc(fpin);
						if(ch == '=')cout<<":="<<"\t2"<<"\t运算符"<<endl;
						else {
							cout<<":"<<"\t2"<<"\t运算符"<<endl;
							fseek(fpin,-1L,SEEK_CUR);
						}
					 }break;
			case '>':{
						ch = fgetc(fpin);
						if(ch == '=')cout<<">="<<"\t2"<<"\t运算符"<<endl;
						else {
							cout<<">"<<"\t2"<<"\t运算符"<<endl;
							fseek(fpin,-1L,SEEK_CUR);
						}
					 }break;
			case '<':{
						ch = fgetc(fpin);
						if(ch == '=')cout<<"<="<<"\t2"<<"\t运算符"<<endl;
						else {
							cout<<"<"<<"\t2"<<"\t运算符"<<endl;
							fseek(fpin,-1L,SEEK_CUR);
						}
					 }break;
			// no recognition
			default: cout<<ch<<"\t6"<<"\t无识别符"<<endl;
		}
	}
}
int main(){
	char input[30];
	FILE *fpin;
	cout<<"Please enter the source file name:\n"<<endl;
	for(;;){
		cin>>input;
		if((fpin = fopen(input,"r")) != NULL)
			break;
		else
			cout<<"Path input error"<<endl;
	}
	cout<<"****************Lexical analysis result********************"<<endl;
	analyze(fpin);
	fclose(fpin);
}

　　operation result: