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词法分析程序实验报告

实验一、词法分析实验

专业:商业软件工程   姓名王芷玲  学号201606110246

一、 实验目的

 

     编制一个词法分析程序。

 

二、 实验内容和要求

     对字符串表示的源程序,从左到右进行扫描和分解,根据词法规则,识别出一个一个具有独立意义的单词符号,以供语法分析之用 发现词法错误,则返回出错信息。。

 

三、 实验方法、步骤及结果测试

 源程序名:压缩包文件(rarzip)中源程序名 ceshi.c

可执行程序名:ceshi.exe

 

  1. 主要程序段及其解释:

实现主要功能的程序段,重要的是程序的注释解释。

#include<stdio.h>

#include<string.h>

char str[100];

char take[8];//存放单词符号的字符串

int sum;//存放整数型单词

char ch;

int zbm;//存放单词字符的种别码

int i,n,p,m=0;//p是缓冲区str的指针,mtake的指针

char *keyword[8]={"begin","if","then","while","do","end","l(l|d)*","dd*"};

void scanner()//词法扫描程序

{

 

   /* for(i=0;i<8;i++)

    {

        take[i]=NULL;

    }

    ch=str[p++];*/

    m=0;

    sum=0;

    for(m=0;m<8;m++)

        take[m]=0;

    ch=str[p++];

 

    while(ch==‘ ‘||ch==‘\n‘)

    {

        ch=str[p++];

    }

    if((ch>=‘a‘&&ch<=‘z‘)||(ch>=‘A‘&&ch<=‘Z‘))//可能是标识符或者是变量名

    {

        m=0;

        while(ch>=‘0‘&&ch<=‘9‘||(ch>=‘a‘&&ch<=‘z‘)||(ch>=‘A‘&&ch<=‘Z‘))

        {

            take[m++]=ch;

            ch=str[p++];

        }

        take[m++]=‘\0‘;

        p--;

        zbm=10;

        for(i=0;i<6;i++)//将识别出的字符和已定义的标符进行比较

            if(strcmp(keyword[i],take==0))

        {

            zbm=i+1;

            break;

        }

    }

    else if(ch>=‘0‘&&ch<=‘9‘)

    {

        while(ch>=‘0‘&&ch<=‘9‘)

        {

            sum=sum*10+ch-‘0‘;

            ch=str[p++];

        }

        p--;

        zbm=11;

    }

    else

    {

        switch(ch)

        {

            case ‘+‘:

                zbm=13;

                take[0]=ch;

                ch=str[p++];

                break;

            case ‘-‘:

                zbm=14;

                take[0]=ch;

                ch=str[p++];

                break;

            case ‘*‘:

                zbm=15;

                take[0]=ch;

                ch=str[p++];

                break;

            case ‘/‘:

                zbm=16;

                take[0]=ch;

                ch=str[p++];

                break;

 

 

            case ‘<‘:

 

                take[m++]=ch;

                ch=str[p++];

                if(ch==‘>‘)

                {

                    zbm=21;

                    take[m++]=ch;

                }

                else if(ch==‘=‘)

                {

                    zbm=22;

                take[m]=ch;

                }

                else{

                    zbm=20;

                    p--;

                }

 

                break;

            case ‘>‘:

                take[0]=ch;

                ch=str[p++];

                if(ch==‘=‘)

                {

                    zbm=24;

                take[0]=ch;

                }

                else{

                    zbm=23;

                    p--;

                }

                break;

            case ‘:‘:

                take[0]=ch;

                ch=str[p++];

                if(ch==‘=‘)

                {

                    zbm=18;

                take[m++]=ch;

                ch=str[p++];

                }

                else{

                    zbm=17;

                    p--;

                }

                break;

 

            case ‘=‘:

                zbm=25;

                take[0]=ch;

                ch=str[p++];

                break;

            case ‘;‘:

                zbm=26;

                take[0]=ch;

                ch=str[p++];

                break;

            case ‘(‘:

                zbm=27;

                take[0]=ch;

                ch=str[p++];

                break;

            case ‘)‘:

                zbm=28;

                take[0]=ch;

                ch=str[p++];

                break;

            case ‘#‘:

                zbm=0;

                take[0]=ch;

                ch=str[p++];

                break;

            default:

                zbm=-1;

 

        }

    }

}

main()

{

 

    int n,i;

    printf("----------------------------------------\n");

    printf("\t编制一个词法分析程序\n\n");

    printf("\t要求:\n");

    printf("\t输入:源程序字符串\n");

    printf("\t输出:二元组(种别,单词本身)\n");

    printf("----------------------------------------\n\n");

 

 

    printf("请输入您要输入的字符:\n");

    do//输入一段字符串

    {

        ch=getchar();

        str[p++]=ch;

    }while(ch!=‘#‘);

 

    p=0;

    ch=str[0];

    if(ch>=‘0‘&&ch<=‘9‘)

        printf("错误!\n");

    else

    {

        do

        {

            scanner();

            switch(zbm)

            {

            case 11:

                printf("(%d,%d)\n",11,sum);

                break;

            case -1:

                printf("错误!\n");

                break;

            default:

                printf("(%d,%s)\n",zbm,take);

            }

        }while(zbm!=0);

    }

    return 0;

}

 

运行结果及分析

技术分享

 

词法分析程序实验报告