实验1_词法分析器.cpp

编写能识别给定的程序设计语言的词法规则

#include <stdio.h>
#include <string.h>
#include <process.h>
#define MAX 100

void main(){
	FILE *in,*out;/*存放输入字符串和输出单词串的文件*/
	int ch;
	char arr[MAX];/*arr数组存放单词符号*/
	char currentchar;/*currentchar存放当前输入字符*/
	int i=0;/*arr数组的一个指针*/


/*以读方式打开输入文件*/
	if((in=fopen("infile.txt","r"))==NULL){
		 printf("can not open file\n");
		  exit(0);
		  }

/*以写方式打开输出文件*/
if((out=fopen("outfile.txt","w"))==NULL){
	 printf("cannout open outfile\n");
	  exit(1);
	  }


//去掉开头空格
currentchar=fgetc(in);

while(currentchar==' '){ 
	 currentchar=fgetc(in);
	 }

while(currentchar!='@'){

/*常数部分判断*/
if((currentchar>='a'&&currentchar<='z')||(currentchar>='A'&&currentchar<='Z')||(currentchar>='0'&&currentchar<='9')||currentchar=='('||currentchar==')'||currentchar=='{'||currentchar=='}'||currentchar=='>'||currentchar=='<'||currentchar==';'||currentchar=='+'||currentchar=='-'||currentchar=='='||(ch=currentchar)=='\n'||currentchar==' '){
	i=0;//清空arr字符数组

	if(currentchar>='0'&&currentchar<='9'){
		arr[i++]=currentchar;
		currentchar=fgetc(in);//再读入下一个字符
		while(currentchar>='0'&&currentchar<='9'){
			arr[i++]=currentchar;
			currentchar=fgetc(in);
			}
		if(currentchar!='.'){ //如果当前读入的符号不为小数点，则常数读完毕，输出此常数
			arr[i++]='\0';
			fprintf(out,"%s%d,%c%s%c%s\n","(",16,'"',arr,'"',")");//格式化输出到目标文件，16代表种别码， arr为内码值，规定用数字本身代表
			}
		else{//当前字符为小数点则继续向下读入
			arr[i++]=currentchar;
			currentchar=fgetc(in);

			while(currentchar>='0'&&currentchar<='9'){
				arr[i++]=currentchar;
				currentchar=fgetc(in);
		}
			arr[i++]='\0';
			fprintf(out,"%s%d,%c%s%c%s\n","(",16,'"',arr,'"',")");
			}

		while(currentchar==' '){
			currentchar=fgetc(in);
			}
		}

/*判断标识符和关键字部分*/
	if((currentchar>='a'&&currentchar<='z')||(currentchar>='A'&&currentchar<='Z')){
		i=0;//清空arr字符数组
		while((currentchar>='a'&&currentchar<='z')||(currentchar>='0'&&currentchar<='9')||(currentchar>='A'&&currentchar<='Z')){
			arr[i++]=currentchar;
			currentchar=fgetc(in);
			}

//把字符数组arr和关键字表比较，判断单词串是关键字还是标识符
    arr[i++]='\0';
	if(strcmp(arr,"BEGIN")==0)
		fprintf(out,"%s%d,%c%s%c%s\n","(",1,'"',arr,'"',")");

	else if(strcmp(arr,"END")==0){
		fprintf(out,"%s%d,%c%s%c%s\n","(",2,'"',arr,'"',")");
		break;}
	else if(strcmp(arr,"IF")==0)
		fprintf(out,"%s%d,%c%s%c%s\n","(",3,'"',arr,'"',")"); 

	else if(strcmp(arr,"THEN")==0)
		fprintf(out,"%s%d,%c%s%c%s\n","(",4,'"',arr,'"',")");

    else if(strcmp(arr,"ELSE")==0)
		fprintf(out,"%s%d,%c%s%c%s\n","(",5,'"',arr,'"',")");

	else if(strcmp(arr,"WHILE")==0)
		fprintf(out,"%s%d,%c%s%c%s\n","(",6,'"',arr,'"',")");

	else if(strcmp(arr,"DO")==0)
		fprintf(out,"%s%d,%c%s%c%s\n","(",7,'"',arr,'"',")");

	else
		fprintf(out,"%s%d,%c%s%c%s\n","(",17,'"',arr,'"',")");

}

	while(currentchar==' '){ 
		currentchar=fgetc(in);
		}


//判断标识符包括：=,+, -, <, >, ;, ., ==.
	if(currentchar=='+'){//+
		fprintf(out,"%s%d,%c%c%c%s\n","(",9,'"',currentchar,'"',")");
		currentchar=fgetc(in);
		}
	while(currentchar==' '){ 
		currentchar=fgetc(in);
		}

	if(currentchar=='.'){//.
		fprintf(out,"%s%d,%c%c%c%s\n","(",14,'"',currentchar,'"',")");
		currentchar=fgetc(in);
		}
	while(currentchar==' '){ 
		currentchar=fgetc(in);
		}


	if(currentchar=='-'){//-
		fprintf(out,"%s%d,%c%c%c%s\n","(",10,'"',currentchar,'"',")");
		currentchar=fgetc(in);
		}
	while(currentchar==' '){ 
		currentchar=fgetc(in);
	}


	if(currentchar=='='){//=
		i=0;
		arr[i++]=currentchar;
		currentchar=fgetc(in);
		if(currentchar=='='){//==
			arr[i++]=currentchar;
			arr[i++]='\0';
			fprintf(out,"%s%d,%c%s%c%s\n","(",12,'"',arr,'"',")");
			currentchar=fgetc(in);
			}
		else{ 
			arr[i++]='\0';
			fprintf(out,"%s%d,%c%s%c%s\n","(",8,'"',arr,'"',")");
		}
	}
	while(currentchar==' '){
		currentchar=fgetc(in);
	}


	if(currentchar==';'){//;
		fprintf(out,"%s%d,%c%c%c%s\n","(",15,'"',currentchar,'"',")");
		currentchar=fgetc(in);
	}
	while(currentchar==' '){ 
		currentchar=fgetc(in);
	}

	if(currentchar=='>'){//>
		fprintf(out,"%s%d,%c%s%c%s\n","(",13,'"',arr,'"',")");
		currentchar=fgetc(in);
		}
	while(currentchar==' '){ 
		currentchar=fgetc(in);
	}


	if(currentchar=='<'){//<
		fprintf(out,"%s%d,%c%s%c%s\n","(",11,'"',arr,'"',")");
		currentchar=fgetc(in);
		}
	while(currentchar==' '){ 
		currentchar=fgetc(in);
	}
	
	while((ch=currentchar)=='\n'){
		currentchar=fgetc(in);
	}
	while(currentchar==' '){
		currentchar=fgetc(in);
	}
}
else{
	fprintf(out,"%s,%c%c%c\n","error",'"',currentchar,'"');
	currentchar=fgetc(in);
}
}//结束开头while语句
/*关闭文件退出*/
fclose(in);
fclose(out);
}