编译原理 | C++ | 简单的词法分析器 (。・∀・)ノ

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

int IsAlpha(char c){
        if(((c<='z')&&(c>='a'))||((c<='Z')&&(c>='A')))
        return 1;
        else return 0;
}
int IsNum(char c){
    if(c>='0'&&c<='9')
    return 1;
    else return 0;
}
int IsBound(char c){
    if(c=='('||c==')'||c==','||c==';'||c=='{'||c=='}'){
        return 1;
    }else return 0;
}
int IsOper(char c){
    if(c=='+'||c=='-'||c=='*'||c=='/'||c=='='||c=='>'||c=='<'||c=='!')
        return 1;
    else return 0;
}
void Scanner(string s){
    char p[20];
    for(int i=0;i<(s.length());i++)
    p[i] = s[i];
    for(int i=s.length();i<20;i++)
    p[i] = '\0';
    int f,t;
    f=0;//word[0]
    t=0;//word[tail]
    while(t<=s.length()){

            if(IsAlpha(p[t])){//首字符是字母
                while(IsAlpha(p[t+1])||IsNum(p[t+1]))
                t++;
            char word[t-f+1];//分出来的字符串
            for(int i=0;i<t-f+1;i++)word[i]=p[f+i];
            word[t-f+1]='\0';
            string st1 = word;//切分出的字符串
            if(st1=="if"||st1=="int"||st1=="for"||st1=="while"||st1=="do"||st1=="return"||st1=="break"||st1=="continue")
                cout<<"(1,\""<<st1<<"\")"<<endl;//识别保留字
            else cout<<"(2,\""<<st1<<"\")"<<endl;//识别标识符
            }
            else//首字符不是字母
                if(IsNum(p[t])){
                    while(IsNum(p[t+1]))
                    t++;
                char word[t-f+1];//分出来的字符串
                for(int i=0;i<t-f+1;i++)word[i]=p[f+i];
                word[t-f+1]='\0';
                string st1 = word;
                cout<<"(3,\""<<st1<<"\")"<<endl;//识别为常数
                }
                else{//首字母不是数字也不是字母
                    if(p[t]==','||p[t]==';'||p[t]=='{'||p[t]=='}'||p[t]=='('||p[t]==')'){
                        cout<<"(5,\""<<p[t]<<"\")"<<endl;//识别为分隔符
                    }
                    else{
                        if(p[t]=='+'||p[t]=='-'||p[t]=='*'||p[t]=='/'||p[t]=='>'||p[t]=='<'||p[t]=='!'){
                            if(p[t+1]=='='&&(p[t]=='>'||p[t]=='<'||p[t]=='!')){
                                cout<<"(5,\""<<p[t]<<p[t+1]<<"\")"<<endl;
                                t++;
                            }else cout<<"(5,\""<<p[t]<<"\")"<<endl;
                        }
                    }
                }
        f=t+1;
        t=f;
    }//end t>s.length()
};
int main(){
    cout<<"输入文件路径+名字"<<endl;
    string fn;
    cin>>fn;
    ifstream fin(fn);
    if (fin.is_open()){
        cout<<"文件读取成功"<<endl;
        string line;
        while (getline(fin,line)){
            Scanner(line);
        }
    }else cout<<"文件读取失败"<<endl;
    return 0;
}