词法分析程序

Input
输入一个小C语言源程序，源程序长度不超过2000个字符，保证输入合法。
Output
按照源程序中单词出现顺序输出，输出二元组形式的单词串。

(单词种类,单词值)

单词一共5个种类：

关键字：用keyword表示
自定义标识符：用identifier表示
整数：用integer表示
界符：用boundary表示
运算符：用operator表示

每种单词值用该单词的符号串表示。

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

void judge(string s)
{
    if(s[0]>='0'&&s[0]<='9') //开头是数字肯定就为数字
    {
        cout<<"(integer,"<<s<<")"<<endl;
    }
    else if(s=="main"||s=="if"||s=="else"||s=="for"||s=="while"||s=="int")
    {
        cout<<"(keyword,"<<s<<")"<<endl;
    }
    else
    {
        cout<<"(identifier,"<<s<<")"<<endl;
    }
}
void lexical_analysis()
{
    string s;
    while(cin>>s)
    {
        int len=s.length();
        string temp="";
        for(int i=0; i<len; i++)
        {

            if(s[i] == '=' || s[i] == '+' || s[i] == '-'||s[i] == '*'
                    || s[i] == '/' || s[i] == '<' || s[i] == '>' || s[i] == '!')
            {
                if(temp.length())
                {
                    judge(temp);
                }
                temp="";
                if(i+1<len&&s[i+1]=='=')
                {
                    cout<<"(operator,"<<s[i]<<s[i+1]<<")"<<endl;
                    i++;
                }
                else
                {
                    cout<<"(operator,"<<s[i]<<")"<<endl;
                }
            }

            else if(s[i] == '(' || s[i] == ')' || s[i] == '{'||s[i] == '}'
                    || s[i] == ',' || s[i] ==';')
            {
                if(temp.length())
                {
                    judge(temp);
                }
                temp="";
                cout<<"(boundary,"<<s[i]<<")"<<endl;
            }

            else
            {
                temp=temp+s[i];
            }
        }
        if(temp.length())
        {
            judge(temp);
        }

    }
}
int main()
{
    lexical_analysis();

    return 0;

}

本文地址：https://blog.csdn.net/fkmmmm/article/details/108565578