Compiler_词法分析_直接转向法

最新推荐文章于 2022-09-06 10:57:16 发布

svitter

最新推荐文章于 2022-09-06 10:57:16 发布

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分类专栏：编译器文章标签： Compiler

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本文详细解析了一段用于分析C++代码中数字字符串的算法，包括其核心逻辑、状态转移过程以及如何判断合法数字。适用于C++初学者及需要深入理解数字字符串解析算法的开发者。

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本文出自：blog.youkuaiyun.com/svitter

依据上述转换图，写出直接转向代码：

//============================================================================
// Name        : Comlier.cpp
// Author      : vit
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
#include <string.h>

using namespace std;

bool confirm;
int status;
int no;

bool JudgeNum(char &a)
{
    if(a >= '0' && a <= '9')
        return true;
    else
        return false;
}


void analysis(string &a)
{
    if(status == 0)
    {
        if(a[no] == '.')
        {
            status = 6;
            no ++;
            analysis(a);
        }
        else if(JudgeNum(a[no]))
        {
            status = 1;
            no ++;
            analysis(a);
        }
        else
        {
            confirm = false;
//            cout << status;
            return;
        }
    }
    else if(status == 1)
    {
        if(JudgeNum(a[no]) || a[no] == '.')
        {
            status = 2;
            no++;
            analysis(a);
        }
        else if(a[no] == 'E'|| a[no] == 'e')
        {
            status = 5;
            no++;
            analysis(a);
        }
        else
        {
            confirm = false;
//            cout << status;
            return ;
        }
    }
    else if(status == 2)
    {
        if(JudgeNum(a[no]))
        {
            status = 2;
            no++;
            analysis(a);
        }
        else if(a[no] == 'E'|| a[no] == 'e')
        {
            status = 3;
            no++;
            analysis(a);
        }
        else
        {
            confirm = true;
//            cout << status;
            return;
        }
    }
    else if(status == 3)
    {
        if(a[no] == '+' || a[no] == '-')
        {
            status = 4;
            no++;
            analysis(a);
        }
        else
        {
            confirm = false;
//            cout << status;
            return;
        }
    }
    else if(status == 4)
    {
        if(JudgeNum(a[no]))
        {
            status = 5;
            no++;
            analysis(a);
        }
        else
        {
            confirm = false;
//            cout << status;
            return;
        }
    }
    else if(status == 5)
    {
        if(JudgeNum(a[no]))
        {
            status = 5;
            no++;
            analysis(a);
        }
        else
        {
            confirm = true;
//            cout << status;
            return;
        }
    }
    else if(status == 6)
    {
        if(JudgeNum(a[no]))
        {
            status = 2;
            no++;
            analysis(a);
        }
        else
        {
            confirm = false;
//            cout << status;
            return;
        }
    }
    else
        cout << "status error." << endl;

}


int main()
{
    string a;
    while(cin >> a)
    {
        confirm = false;
        status = 0;
        no = 0;
        analysis(a);
        if(confirm)
            cout << "yes" << endl;
        else
            cout << "no" << endl;
    }
}