PL0语言单词的词法分析程序_pl0源程序词法分析的代码-优快云博客

本文链接：https://blog.youkuaiyun.com/ajaxhe/article/details/4770553

本文展示了如何编写一个PL0语言的词法分析程序，包括处理各种符号、保留字和数字，并提供了一个简单的读取源代码并输出符号类型的示例。程序通过读取'in.txt'文件进行分析，并将结果输出到'result.txt'。

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/*前段时间在编译原理实验上写了一个PL0语言单词的词法分析程序，把源代码付上，供初学者参考。也欢迎大侠们提出宝贵的意见*/

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

//设置单字符符号
char symbol[] = {'+','-','*','/','(',')','=',',','.','#',';'};
//设置单字符名称
string ssym[] = {"plus","minus","times","slash","lparen","rparen","eql","comma","peroid","neg","semicolon"};
//设置保留字
string word[] = {"begin","call","const","do","end","if","odd","procedure","read","then","var","while","write"};
//设置保留字符号
string wsym[] = {"beginsym","callsym","constsym","dosym","endsym","ifsym","oddsym","procsym","readsym","thensym","varsym","whilesym","writesym"};

ifstream fin("in.txt");
ofstream fout("result.txt");

void judgeWord(string str);//搜索当前符号是否为保留字
int judgeSymbol(char ch);//搜索当前符号是否为单字符符号
void getsym();//词法分析，获取一个符号

int main(){
    getsym();//词法分析，获取一个符号
    return 0;
}

void getsym(){
    char ch;
    ch = fin.get();
    while(ch != '#'){
        if(ch>='a' && ch<='z'){//名字或保留字以a..z开头
            string strTemp = "";
            do{
                strTemp = strTemp + ch;
                ch = fin.get();
            } while(ch>='a' && ch<='z' || ch>='0' && ch<='9');
            judgeWord(strTemp);//搜索当前符号是否为保留字
        }
        else{
            if(ch>='0' && ch<='9'){//检测是否为数字：以0..9开头
                double num = 0.0;
                do{
                    num = 10 * num + ch - '0';//将形如："12345"的字符串装换车long类型的12345
                    ch=fin.get();
        &n