compiler.cpp

这个程序是编译程序的一部分

#include <iostream.h>
#include <string.h>
#include <stdio.h>
#include <process.h>

int i,j; 
char c[20];
FILE *fp;
FILE *result;

int compare1(char ch) //compare single character
{
  if ('0'<=ch&&ch<='9')
    return 1; //digit
  else
    if (('A'<=ch&&ch<='Z')||('a'<=ch&&ch<='z'))
      return 2; //letter
    else
      return 0; //other
}

int compare2(char *c) //keywords and symbol
{
  if(strcmp(c,"main")&&strcmp(c,"if")&&strcmp(c,"then")&&strcmp(c,"else")&&strcmp(c,"while")&&strcmp(c,"do")&&strcmp(c,"int"))
    return 1;
  else
    return 0; // same means 0
}

void scan(char &ch)
{
  if(compare1(ch)==2) //1st character is letter
  {    
    i=1;
    c[0]=ch;
    ch=fgetc(fp);
    while(compare1(ch)>0)
    {
      c[i++]=ch;
      ch=fgetc(fp);
    }
    c[i]='\0';
    if (!compare2(c))
    {
      cout<<"<"<<c<<",->"<<endl; //keyword
      fprintf(result,"<%s,->\n",c);
    }
    else 
    {
      cout<<"<0,"<<c<<">"<<endl; //symbol
      fprintf(result,"<0,%s>\n",c);
    }
  }
  else if(compare1(ch)==1) //1st char is digit then it is number
  {
    if('1'<=ch&&ch<='9') //1st char is 1-9 means decimal (10 based)
    {
      j=1;
      c[0]=ch;
      ch=fgetc(fp);
      i=1;
      while(compare1(ch)==1)
      {
        c[i++]=ch;
        ch=fgetc(fp);
      }
      c[i]='\0';
    }
    else if(ch=='0') //1st char is 0 means 8/16 based
    {
      ch=fgetc(fp); // point to 2nd char
      //if(compare1(ch)==1) //if 2nd char is digit then >0 or else =0
      i=0;
      if(ch=='x')
      {
        ch=fgetc(fp);
        j=3;     
        while(compare1(ch)==1||(ch<='f'&&ch>='a'))
        {
          c[i++]=ch;   
          ch=fgetc(fp);
        }
        c[i]='\0';
      } //2nd char is x means 16 based or else 8 based
      else if(compare1(ch)==1)
      {
        j=2; //8-base means type 2
        while(compare1(ch)==1)
        {
          c[i++]=ch;   
          ch=fgetc(fp);
        }
        c[i]='\0';
      }
      else
      {
        j=0;
        ch='0';
        i=1;
        cout<<"<1,0>"<<endl;
        fprintf(result,"<%d,%s>\n",i,c);
        ch=fgetc(fp);
      }    
    }
    if(j)
    {
      cout<<"<"<<j<<","<<c<<">"<<endl; //output value
      fprintf(result,"<%d,%s>\n",j,c);
    }
  }
  else if (ch!=' '&&ch!='\n'&&ch!='\t')
  {  
    cout<<"<"<<ch<<",->"<<endl;
    fprintf(result,"<%c,->\n",ch);
    ch=fgetc(fp);
  }
  else ch=fgetc(fp);
}

void main ()
{
  char ch;

  if((fp=fopen("system.txt","r"))==NULL)
  {
    printf("<system.txt> not opened.\n");
    exit(0);
  }
  result=fopen("result.txt","w");
  ch=fgetc(fp);
  while(ch!=EOF)
    scan(ch);
}