实验2《词法分析程序设计与实现》（C语言版）-Toy模板网

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正文

任务描述

本关任务：加深对词法分析器的工作过程的理解；加强对词法分析方法的掌握；能够采用一种编程语言实现简单的词法分析程序；能够使用自己编写的分析程序对简单的程序段进行词法分析。

编程要求

根据提示，在右侧编辑器补充代码标示符、数字符及其他字符符号的识别程序后，点击评测运行程序，系统会自动进行结果对比。

测试说明

平台会对你编写的代码进行测试：

测试输入：

    using namespace std;
    int main()
    {
        int year;
        cout << "hello" << endl;
        return 0;
    }
    #

开始你的任务吧，祝你成功！

实验答案

#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
char prog[80], token[20];
char ch;
int syn, p, m = 0, n, row, sum = 0;
const char* rwtab[8] = { "if","int","for","while","do","return","break","continue" };
const char* rwtab1[8] = { "main","a","b","c","d","e","f","g" };

void scaner()
{
	/*
		共分为三大块，分别是标示符、数字、符号，对应下面的 if   else if  和 else
	*/
	for (n = 0; n < 8; n++) token[n] = NULL;
	ch = prog[p++];
	while (ch == ' ')
	{
		ch = prog[p];
		p++;
	}
	if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) {
		m=0;
		while(1){
			if((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) {
				token[m++]=ch;
				ch=prog[p++];

			}else{
				p--;
				break;
			}
		}
		token[m]='\0';
		syn=0;
		for(n=0;n<8;n++){
			if (strcmp(token, rwtab1[n]) == 0)
			{
				syn = 2;
				break;
			}
			else if (strcmp(token, rwtab[n]) == 0) {
				syn = 1;
				break;
			}
		}	
		if(!syn)syn=2;		

	}else if ((ch >= '0' && ch <= '9')) {
		syn=3;
		sum=ch-'0';
	}
	else switch (ch)   //其他字符 
	{
		case'<':m = 0; token[m++] = ch;
				ch = prog[p++];
				if (ch == '>')
				{
					syn = 4;
					token[m++] = ch;
				}
				else if (ch == '=')
				{
					syn = 4;
					token[m++] = ch;
				}
					else
					{
						syn = 4;
						p--;
					}
					break;
			case'>':m = 0; token[m++] = ch;
					ch = prog[p++];
					if (ch == '=')
					{
						syn = 4;
						token[m++] = ch;
					}
					else
					{
						syn = 4;
						p--;
					}
					break;
			case':':m = 0; token[m++] = ch;
					ch = prog[p++];
					if (ch == '=')
					{
						syn = 4;
						token[m++] = ch;
					}
					else
					{
						syn = 4;
						p--;
					}
					break;
			case'*':syn = 4; token[0] = ch; break;
			case'/':syn = 4; token[0] = ch; break;
			case'+':syn = 4; token[0] = ch; break;
			case'-':syn = 4; token[0] = ch; break;
			case'=':syn = 4; token[0] = ch; break;
			case';':syn = 5; token[0] = ch; break;
			case',':syn = 5; token[0] = ch; break;
			case'(':syn = 5; token[0] = ch; break;
			case')':syn = 5; token[0] = ch; break;
			case'{':syn = 5; token[0] = ch; break;
			case'}':syn = 5; token[0] = ch; break;
			case'#':syn = 0; token[0] = ch; break;
			case'\n':syn = -2; break;
			default: syn = -1; break;
	}

}
	



int main()
{
	p = 0;
	row = 1;
	cout << "Please input string:" << endl;
	do
	{
	cin.get(ch);
	prog[p++] = ch;
	} while (ch != '#');
	p=0;
    do{
      scaner();
	  //cout<<syn<<endl;
	  //cout<<syn<<endl;
      switch (syn)
      {
		case 0: break;
		case 3: cout << "(" << syn << "," << sum << ")" << endl; break;
		case -1: cout << "Error in row " << row << "!" << endl; break;
		case -2: row = row++; break;
		default: cout << "(" << syn << "," << token << ")" << endl; break;
      }
	  //cout<<row<<endl;
	  if(syn==-2)row++;
    } while (syn != 0); 
}