词法分析

#include<stdio.h>
#include<string.h>
char prog[800],token[20];
char ch;
int syn,p,m,sum;
char *rwtab[6]={"begin","if","then","while","do","end"};

scaner()
{
	int n;
	for(n=0;n<20;n++)
	m=0;
	sum=0;
	ch=prog[p++];
	while(ch>='a'&&ch<='z')
	{
		ch=prog[p++];
	}
	if(ch>='a'&&ch<='z'||ch>='0'&&ch<='9')
	{
		token[m++]=ch;
		ch=prog[p++];
	}
	syn=10;
	p--;
	for(n=0;n<6;n++)//标识符是否为关键词
	{
		if(strcmp(token,rwtab[n])==0)
		{
			syn=n+1;
			break;
		}
		else if
		{
			if(ch>='0'&&ch<='9')
			{
				sum=sum*10+(ch-'0');
				ch=prog[p++];
			}
			syn=11;
			p--;       
		}
		else 
		{
			switch(ch)
		{
			case '<':
				token[m++]=ch;
				ch=prog[p++];
				if(ch='>')
				{
					syn=21;
					token[m++]=ch;
				}
				else if(ch=='=')
				{
					syn=22;
					token[m++]=ch;
				}
				else
				{syn=20;
				p--;
				}break;
			case '>':m=0;
				token[m++]=ch;
				ch=prog[p++];
				if(ch=='=')
				{
					syn=24;token[m++]=ch;
				}
				else
				{
					syn=23;p--;
				}
				break;
			case ':':
				m=0;token[m++]=ch;
				ch=prog[p++];
				if(ch=='=')
				{
					syn=18;
					token[m++]=ch;
				}
				else
				{
					syn=17;
					p--;
				}
				break;
			case '+':syn=13;token[0]=ch;break;
			case '-':syn=14;token[0]=ch;break;
			case '*':syn=15;token[0]=ch;break;
			case '/':syn=16;token[0]=ch;break;
			case '=':syn=25;token[0]=ch;break;
			case ';':syn=26;token[0]=ch;break;
			case '(':syn=27;token[0]=ch;break;
		    case ')':syn=28;token[0]=ch;break;
			case '#':syn=0; token[0]=ch;break;
			default: syn=-1;token[0]=ch;
		}
	}

main()
{
	p=0;
	printf("\n请输入源程序段");
	do{
		ch=getchar();
		prog[p++]=ch;
	}while(ch!='#');
	p=0;
	do{
		scaner();//读取一个单词符号，类型syn，单词token或sum
		switch(syn)
		{
		case 11:printf("\n(%d,%d)",syn,sum);
			break;
		case -1:printf("\n(%s,出错！)",token);
			break;
		default:printf("\n(%d,%s)",syn,token);
		}
	}while(syn!=0);
	System("pause");
}