word.cpp

为L语言设计一个语法分析器。 读入源程序

/*本词法分析器功能：将从制定文件读取的程序段的单词、符号识别出并存入save文件，另外也将数字
从字符串格式转化为整型或浮点型格式，同样存入文件，按顺序，如果存在文法中不允许的字符将会报错
和提示*/
#include<iostream.h>
#include<fstream.h>
#include<stdlib.h>
#include<string.h>
#include<stdio.h>
FILE *fp;

int IsLetter(char ch)
{
	if(ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z') return 1;
	else return 0;
}

int IsDigit(char ch)
{
	if(ch >= '0' && ch <= '9') return 1;
	else return 0;
}

int main()
{
	ofstream outFile("save.txt");
	if(!outFile){
		cerr<< "cannot" << endl;
		exit(1);
	}

	char ch;
	char fname[20];
	char save[15];
	int i = 0, j = 0, digit = 0; 
	float digitf = 0, e = 1;
	int a[10];
	int error = 0;
	cout << "Please input file name : " ;
	cin >> fname;
	if((fp = fopen(fname, "r+")) == NULL){
		printf("Cannot open the file!\n");
		return 0;
	}

//0
	while((ch = fgetc(fp)) != EOF)
	{
		//cout << ch;
		if(IsLetter(ch))    //1
		{		
			while(IsLetter(ch) || IsDigit(ch))
			{
				save[i++] = ch;
				ch = fgetc(fp);		
			}
			save[i] = '\0';
			if(!strcmp(save,"program"))
				outFile << save << endl;
			else if(!strcmp(save,"begin"))
				outFile << save << endl;
			else if(!strcmp(save,"end"))
				outFile << save << endl;
			else if(!strcmp(save,"const"))
				outFile << save << endl;
			else if(!strcmp(save,"int"))
				outFile << save << endl;
			else if(!strcmp(save,"array"))
				outFile << save << endl;
			else if(!strcmp(save,"if"))
				outFile << save << endl;
			else if(!strcmp(save,"then"))
				outFile << save << endl;
			else if(!strcmp(save,"while"))
				outFile << save << endl;
			else if(!strcmp(save,"do"))
				outFile << save << endl;
			else if(!strcmp(save,"for"))
				outFile << save << endl;
			else if(!strcmp(save,"to"))
				outFile << save << endl;
			else outFile << '%' << save << endl; //写文件         //2
			//save[0] = '\0';
			if(ch == EOF) break;
			i = 0;
			fseek(fp,-1L,SEEK_CUR);
		}
		else if(IsDigit(ch)) //3
		{
			while(IsDigit(ch))
			{
				a[j++] = ch - 48;
				//outFile << a[j-1] << "#" << endl;
				ch = fgetc(fp);  //0~9的ASCII码是48~57				
			}
			for(int k =j-1; k >= 0; k--)
			{
				//outFile << a[k];
				digit += a[k] * e;
				e = e * 10;
			}
			if(ch != '.')
				outFile << digit << endl; //!!!已换算成数字 //4
			else
			{
				a[10] = 0;
				j = 0;
				e = 1; //清空
				ch = fgetc(fp);
				while(IsDigit(ch))
				{
					a[j++] = ch - 48;
					ch = fgetc(fp);
				}
				for(k =0; k <= j-1; k++)
				{
					//outFile << a[k];
					e = e / 10;
					digitf += a[k] * e;					
				}
				digitf = digitf + digit;
				outFile << digitf << endl;
			}
			a[10] = 0;
			j = 0;
			digit = 0;
			e = 1;
			fseek(fp,-1L,SEEK_CUR);   //清零工作
		}
		else if(ch == '+') //5
			outFile << "+" << endl;
		else if(ch == '-') //6
			outFile << "-" << endl;
		else if(ch == '*') //7
			outFile << "*" << endl;
		else if(ch == '/') //8
			outFile << "/" << endl;
		else if(ch == '=') //9
			outFile << "=" << endl;
		else if(ch == ':')       //10
		{
			ch = fgetc(fp);
			if(ch == '=')
				outFile << ":=" << endl; //11
			else
			{
				outFile << ":" << endl;//为语法分析器而改 cout << "There exists a sign which cannot be recognized  :" << endl; // 22 也可以考虑break 然后在程序最后报错
				fseek(fp,-1L,SEEK_CUR);
			}
		}
		else if(ch == '<') //12
		{
			ch = fgetc(fp);
			if(ch == '=')
				outFile << "<=" << endl; //13
			else if(ch == '>')
				outFile << "<>" << endl; //14
			else outFile << "<" << endl; //15

		}
		else if(ch == '>') //16
		{
			ch = fgetc(fp);
			if(ch == '=') //17
				outFile << ">=" << endl;
			else 
			{
				outFile << ">" << endl; //18
				fseek(fp,-1L,SEEK_CUR);
			}
		}
		else if(ch == '(')
			outFile << "(" << endl; //19
		else if(ch == ')')
			outFile << ")" << endl; //20
		else if(ch == '[')
			outFile << "[" << endl; //21
		else if(ch == ']')
			outFile << "]" << endl; //22 
		else if(ch == ';')
			outFile << ";" << endl; //为语法分析时加的!
		else if(ch == ',')
			outFile << "," << endl; //为语法分析时加的!
		else if(ch != ' ' && ch != '\n' && ch != '\t')  //0
		{
			cout << "There exists a sign which cannot be recognized  " << ch << endl; //23
			error = 1;
		}
	}
	outFile << "#";
	fclose(fp);
	if(error == 1)
		cout << "You should have a check on your program." << endl << "But you also have the words analyzed in the file: save.txt! " << endl;	
	else
		cout << "Succeed! The words have been output into the file: save.txt ! :)" << endl;
	return 1;
}
	/*ofstream outFile("save.txt");
	if(!outFile){
		cerr<< "cannot" << endl;
		exit(1);
	}
	int n = 50;
	float f = 20.3;
	outFile << "n:" << n << endl;
	outFile << "f:" << f << endl;*/


// 0372283 王茜