编译原理—递归下降分析

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/*（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]='#';}
运行结果：
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！
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