编译原理—递归下降分析

「爱情、让人受尽委屈。」 2022-08-23 09:56 198阅读 0赞

/*
    （1）E→TG
    （2）G→ATG
    （3）G→ε
    （4）T→FH
    （5）H→MFH
    （6）H→ε
    （7）F→i
    （8）A→+
    （9）A→-
    （10）M→*
    （11）M→/
    */
    #include <iostream>
    #include <fstream>
    #include <dos.h>
    #include <cstring>
    #include <stdlib.h>
    using namespace std;
    char a[100], b[100], d[500], e[10];
    char ch;
    int n1,i1=0,flag=1,n=5;
    
    int E1();
    int E();
    int G();
    int T();
    int H();
    int F();
    int A();
    int M();
    void input();
    void input1();
    void output();
    
    //================================================
    int main()                      /*递归分析*/
    {
        int p;
        char x;
        d[0]='E';
        d[1]='=';
        d[2]=' ';
        d[3]='T';
        d[4]='G';
        d[5]='#';
        //从文件中读入除换行符之外的字符
        ifstream infile("data.txt",ios::in);
        if(!infile)
        {
            cerr<<"open error!"<<endl;
            exit(1);
        }
        char c='c',f[50]= {""};
        int i=0,k=0,l=0;
        while(infile.peek()!=EOF)
        {
            infile.get(c);
            if(c!='\n')
            {
                f[i]=c;
                i++;
            }
        }
        //给操作数组a赋初值，依次进行操作
        do
        {
            a[k]=f[l];
            if(f[l]=='#')
            {
                cout<<"从文件读入字符串(长度<50,以#号结束）\n";
                for(int j=0; a[j]!='\0'; j++)
                    cout << a[j];
                n1=i;
                ch=b[0]=a[0];
                cout<<"\n文法\t分析串\t\t分析字符\t剩余串\n";
                E1();
                if (ch=='#')
                {
                    cout<<"accept"<<endl;
                    p=0;
                    x=d[p];
                    while(x!='#')
                    {
                        cout<<x;
                        p=p+1;
                        x=d[p];          /*输出推导式*/
                    }
                }
                else
                {
                    cout<<"error"<<endl;
                    cout<<"回车返回"<<endl;
                    return (0);
                }
                cout<<endl;
                cout<<"继续>>>>\n"<<endl;
                memset(a,'\0',sizeof(a));
                memset(b,'\0',sizeof(b));
                memset(e,'\0',sizeof(e));
                i1=0,flag=1,n=5;
                k=-1;
            }
            k++;
            l++;
        }
        while(f[l]!='\0');
        infile.close();
        return 0;
    }
    
    //================================================
    int E1()
    {
        int f,t;
        cout<<"E->TG\t";
        flag=1;
        input();
        input1();
        f=T();
        if (f==0)
            return(0);
        t=G();
        if (t==0)
            return(0);
        else
            return(1);
    }
    
    //================================================
    int E()
    {
        int f,t;
        cout<<"E->TG\t";
        e[0]='E';
        e[1]='=';
        e[2]=' ';
        e[3]='T';
        e[4]='G';
        e[5]='#';
        output();
        flag=1;
        input();
        input1();
        f=T();
        if (f==0)
            return(0);
        t=G();
        if (t==0)
            return(0);
        else
            return(1);
    }
    
    //================================================
    int G()
    {
        int f,t,g;
        if(ch=='+'||ch=='-')
        {
            cout<<"G→ATG\t";
            e[0]='G';
            e[1]='=';
            e[2]=' ';
            e[3]='A';
            e[4]='T';
            e[5]='G';
            e[6]='#';
            output();
            flag=1;
            input();
            input1();
            f=A();
            if (f==1)
            {
                t=T();
                if(t==0)
                {
                    cout<<"error"<<endl;
                    return (0);
                }
                g=G();
                if (g==0)
                    return(0);
                return(1);
            }
        }
        cout<<"G->^\t";
        e[0]='G';
        e[1]='=';
        e[2]=' ';
        e[3]='^';
        e[4]='#';
        output();
        flag=1;
        input();
        input1();
        return(1);
    }
    
    //================================================
    int T()
    {
        int f,t;
        printf("T->FH\t");
        e[0]='T';
        e[1]='=';
        e[2]=' ';
        e[3]='F';
        e[4]='H';
        e[5]='#';
        output();
        flag=1;
        input();
        input1();
        f=F();
        if (f==0) return(0);
        t=H();
        if (t==0) return(0);
        else return(1);
    }
    
    //================================================
    int H()
    {
        int f,t,g;
        if(ch=='*'||ch=='/')
        {
            cout<<"H->MFH\t";
            e[0]='H';
            e[1]='=';
            e[2]=' ';
            e[3]='M';
            e[4]='F';
            e[5]='H';
            e[6]='#';
            output();
            flag=1;
            input();
            input1();
            f=M();
            if (f==1)
            {
                t=F();
                if(t==0)
                {
                    cout<<"error"<<endl;
                    return (0);
                }
                g=H();
                if (g==0)
                    return(0);
                return(1);
            }
        }
    
        cout<<"H->^\t";
        e[0]='H';
        e[1]='=';
        e[2]=' ';
        e[3]='^';
        e[4]='#';
        output();
        flag=1;
        a[i1]=ch;
        input();
        input1();
        return(1);
    }
    
    //================================================
    int F()
    {
        if(ch=='i')
        {
            b[i1]=ch;
            cout<<"F->i\t";
            e[0]='F';
            e[1]='=';
            e[2]=' ';
            e[3]='i';
            e[4]='#';
            output();
            flag=0;
            input();
            input1();
            ch=a[++i1];
        }
        else
        {
            cout<<"error\n";
            return(0);
        }
        return(1);
    }
    
    //================================================
    int A()
    {
        if(ch=='+')
        {
            b[i1]=ch;
            cout<<"A->+\t";
            e[0]='A';
            e[1]='=';
            e[2]=' ';
            e[3]='+';
            e[4]='#';
            output();
            flag=0;
            input();
            input1();
            ch=a[++i1];
        }
        else if(ch=='-')
        {
            b[i1]=ch;
            cout<<"A->-\t";
            e[0]='A';
            e[1]='=';
            e[2]=' ';
            e[3]='-';
            e[4]='#';
            output();
            flag=0;
            input();
            input1();
            ch=a[++i1];
        }
        else
        {
            cout<<"error\n";
            return(0);
        }
        return(1);
    }
    
    //================================================
    int M()
    {
        if(ch=='*')
        {
            b[i1]=ch;
            cout<<"M->*\t";
            e[0]='M';
            e[1]='=';
            e[2]=' ';
            e[3]='*';
            e[4]='#';
            output();
            flag=0;
            input();
            input1();
            ch=a[++i1];
        }
        else if(ch=='/')
        {
            b[i1]=ch;
            cout<<"M->/\t";
            e[0]='M';
            e[1]='=';
            e[2]=' ';
            e[3]='/';
            e[4]='#';
            output();
            flag=0;
            input();
            input1();
            ch=a[++i1];
        }
        else
        {
            cout<<"error\n";
            return(0);
        }
        return(1);
    }
    
    //================================================
    void input()
    {
        for (int j=0; j<=i1-flag; j++)
            cout<<b[j];                /*输出分析串*/
        cout<<"\t\t";
        cout<<ch<<"\t\t";                  /*输出分析字符*/
    }
    
    //================================================
    void input1()
    {
        for (int j=i1+1-flag; j<n1; j++)
            cout<<a[j];                 /*输出剩余字符*/
        cout<<endl;
    }
    
    //================================================
    void output()                               /*推导式计算*/
    {
        int m,k,j,q;
        int i=0;
        m=0;
        k=0;
        q=0;
        i=n;
        d[n]='=';
        d[n+1]=' ';
        d[n+2]='#';
        n=n+2;
        i=n;
        i=i-2;
        while(d[i]!=' '&&i!=0)
            i=i-1;
        i=i+1;
        while(d[i]!=e[0])
            i=i+1;
        q=i;
        m=q;
        k=q;
        while(d[m]!=' ')
            m=m-1;
        m=m+1;
        while(m!=q)
        {
            d[n]=d[m];
            m=m+1;
            n=n+1;
        }
        d[n]='#';
        for(j=3; e[j]!='#'; j++)
        {
            d[n]=e[j];
            n=n+1;
        }
        k=k+1;
        while(d[k]!='=')
        {
            d[n]=d[k];
            n=n+1;
            k=k+1;
        }
        d[n]='#';
    }

![Center][]

运行结果：

![Center 1][]

学习心得：  
通过这次实验，真的学到了不少东西。有些看似很好敲的代码，真正实现起来是非常的麻烦，也许是自己的专业水平还有些差距。

不管怎么说，经过千辛万苦终于还是写出来了，自己是最棒的！

[Center]: /images/20220721/bf302dd5f3994a2fab7ea12bc676306f.png
[Center 1]: /images/20220721/217202fa5ed14105bf6a0de4e987877e.png