C语言实现词法分析器

#include <iostream>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
using namespace std;

//关键字 
string key[6]={"main","int","if","else","while","do"}; 
//关键字的种别码
int keyNum[6]={1,2,3,4,5,6}; 
//运算符和界符 
string symbol[17]={"<",">","!=",">=","<=","==",",",";","(",")","{","}","+","-","*","/","="};
//char symbol[12]={'<','>','!=','>=','<=','==',',',';','(',')','{','}'};
//运算符和界符的种别码 
int symbolNum[17]={7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23};
//存放文件取出的字符 
string letter[1000];
//将字符转换为单词
string words[1000];
int length; //保存程序中字符的数目 
int num;

int isSymbol(string s){ //判断运算符和界符 
 int i;
 for(i=0;i<17;i++){
  if(s==symbol[i])
   return symbolNum[i]; 
 }
 return 0;
} 

//判断是否为数字 
bool isNum(string s){
 if(s>="0" && s<="9")
  return true;
 return false;
}

//判断是否为字母 
bool isLetter(string s)
{
 if(s>="a" && s<="z")
  return true;
 return false;
}

//判断是否为关键字,是返回种别码 
int isKeyWord(string s){
 int i;
 for(i=0;i<6;i++){
  if(s==key[i])
   return keyNum[i];
 }
 return 0;
}

//返回单个字符的类型 
int typeword(string str){
 if(str>="a" && str<="z") // 字母 
  return 1;

 if(str>="0" && str<="9") //数字 
  return 2;

 if(str==">"||str=="="||str=="<"||str=="!"||str==","||str==";"||str=="("||str==")"||str=="{"||str=="}"
  ||str=="+"||str=="-"||str=="*"||str=="/") //判断运算符和界符 
  return 3; 

}

string identifier(string s,int n){
 int j=n+1;
 int flag=1;

 while(flag){
  if(isNum(letter[j]) || isLetter(letter[j])){
   s=(s+letter[j]).c_str();
   if(isKeyWord(s)){
    j++;
    num=j;
    return s;
   }
   j++;
  }
  else{
   flag=0;
  }
 } 

 num=j;
 return s;
}

string symbolStr(string s,int n){
 int j=n+1;
 string str=letter[j];
 if(str==">"||str=="="||str=="<"||str=="!") {
  s=(s+letter[j]).c_str();
  j++;
 }
 num=j;
 return s;
}

string Number(string s,int n){
 int j=n+1;
 int flag=1;

 while(flag){
  if(isNum(letter[j])){
   s=(s+letter[j]).c_str();
   j++;
  }
  else{
   flag=0;
  }
 }

 num=j;
 return s;
}

void print(string s,int n){
 cout<<"("<<s<<","<<n<<")"<<endl;
}

void TakeWord(){ //取单词 
 int k;

 for(num=0;num<length;){
  string str1,str;
  str=letter[num];
  k=typeword(str);
  switch(k){
   case 1:
    {
     str1=identifier(str,num);
     if(isKeyWord(str1))
      print(str1,isKeyWord(str1));
     else
      print(str1,0);
     break;
    }

   case 2:
    {
     str1=Number(str,num);
     print(str1,24);
     break;
    }

   case 3:
    {
     str1=symbolStr(str,num);
     print(str1,isSymbol(str1));
     break; 
    }

  }

 } 
}

int main(){
 char w;
 int i,j;

 freopen("s.txt","r",stdin);
 freopen("result.txt","w",stdout); //从控制台输出，而不是文本输出

 length=0;
 while(cin>>w){
  if(w!=' '){
   letter[length]=w;
   length++;
  } //去掉程序中的空格
 }

 TakeWord();
// for(j=0;j<length;j++){
//  cout<<letter[j]<<endl;
// } 

 fclose(stdin);//关闭文件 
 fclose(stdout);//关闭文件 
 return 0;
}