C code works fine when run on turbo c with windows but goes to infinite loop in gcc linux [on hold]

Question

C code works fine when run on turbo c with windows but goes to infinite loop in gcc linux.

I tried to run the code first in gcc compiler in my ubuntu and it went on an infinite loop, some kind of overflow error. So i tried the same in turbo c in windows and it worked fine. Later i also realised that not all compilers in windows are supporting this and they also going to infinite loop.

This is the code:

'''

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

 void chk_label();
 void chk_opcode();
 void READ_LINE();
 struct optab
 {
   char  code[10],objcode[10];
 }myoptab[3]={
           {"LDA","00"},
           {"JMP","01"},
           {"STA","02"}
        };
 struct symtab{
           char symbol[10];
           int addr;
        }mysymtab[10];
 int startaddr,locctr,symcount=0,length;
 char line[20],label[8],opcode[8],operand[8],programname[10];
         void PASS1()
          {
             FILE *input,*inter;                  
             input=fopen("input.txt","r");              
             inter=fopen("inter.txt","w");
             printf("LOCATION LABEL\tOPERAND\tOPCODE\n");
             printf("_____________________________________");            
             fgets(line,20,input);
            READ_LINE();
            if(!strcmp(opcode,"START"))
            {
             startaddr=atoi(operand);
             locctr=startaddr;          
            strcpy(programname,label);
               fprintf(inter,"%s",line);
             fgets(line,20,input);
             }
            else
            {
              programname[0]='\0';
              startaddr=0;
              locctr=0;
            }
              printf("\n %d\t %s\t%s\t %s",locctr,label,opcode,operand);
               while(strcmp(line,"END")!=0)
              {
                   READ_LINE();
                   printf("\n %d\t %s \t%s\t %s",locctr,label,opcode,operand);
                   if(label[0]!='\0')chk_label();
                   chk_opcode();
                   fprintf(inter,"%s %s %s\n",label,opcode,operand);
                   fgets(line,20,input);
              }
           printf("\n %d\t\t%s",locctr,line);
           fprintf(inter,"%s",line);
           fclose(inter);
           fclose(input);
            }
      void PASS2()
      {
         FILE *inter,*output;
         char record[30],part[6],value[5];
         int currtxtlen=0,foundopcode,foundoperand,chk,operandaddr,recaddr=0;
         inter=fopen("inter.txt","r");
         output=fopen("output.txt","w");
         fgets(line,20,inter);
         READ_LINE();
         if(!strcmp(opcode,"START")) fgets(line,20,inter);
         printf("\n\nCorresponding Object code is..\n");
         printf("\nH^ %s ^ %d ^ %d ",programname,startaddr,length);
         fprintf(output,"\nH^ %s ^ %d ^ %d ",programname,startaddr,length);
         recaddr=startaddr; record[0]='\0';
         while(strcmp(line,"END")!=0)
              {
                        operandaddr=foundoperand=foundopcode=0;
                        part[0]= value[0]='\0';
                        READ_LINE();
       for(chk=0;chk<3;chk++)
        {
         if(!strcmp(opcode,myoptab[chk].code))
         {                  
         foundopcode=1;
         strcpy(part,myoptab[chk].objcode);
        if(operand[0]!='\0')
        {
        for(chk=0;chk<symcount;chk++)
        if(!strcmp(mysymtab[chk].symbol,operand))
        {
        itoa(mysymtab[chk].addr,value,10);
        foundoperand=1;
        }
        if(!foundoperand)strcpy(value,"err");
        }
        }
        }
         if(!foundopcode)
         {
                 if(strcmp(opcode,"BYTE")==0 || strcmp(opcode,"WORD")||strcmp(opcode,"RESB"))
                 {strcpy(value,operand);
                }}
         if((currtxtlen+strlen(value)+strlen(part))<=8)
         {
         strcat(record,"^");
         strcat(record,part);
         strcat(record,value);
         currtxtlen+=(strlen(value)+strlen(part));
         }
         else
         {
          printf("\nT^ %d ^%d ^%s",recaddr,currtxtlen,record);
          fprintf(output,"\nT^ %d ^%d ^%s",recaddr,currtxtlen,record);
          recaddr+=currtxtlen;
          currtxtlen=strlen(value)+strlen(part);
          strcpy(record,part);
          strcat(record,value);
         }
      fgets(line,20,inter);
         }  
            printf("\nT^ %d ^%d %s",recaddr,currtxtlen,record);
            fprintf(output,"\nT^ %d ^%d %s",recaddr,currtxtlen,record);
            printf("\nE^ %d\n",startaddr);
            fprintf(output,"\nE^ %d\n",startaddr);
            fclose(inter);
            fclose(output);
     }      
     void READ_LINE()
     {
       char buff[8],word1[8],word2[8],word3[8];
       int i,j=0,count=0;
        label[0]=opcode[0]=operand[0]=word1[0]=word2[0]=word3[0]='\0';
          for(i=0;line[i]!='\0';i++)
            {
           if(line[i]!=' ')buff[j++]=line[i];
           else
            {
            buff[j]='\0';
            strcpy(word3,word2);strcpy(word2,word1);strcpy(word1,buff);
            j=0;count++;
            }
            }
            buff[j-1]='\0';
            strcpy(word3,word2);
            strcpy(word2,word1);
            strcpy(word1,buff);
           switch(count)
             {
                   case 0:strcpy(opcode,word1);break;
                   case 1:{strcpy(opcode,word2);strcpy(operand,word1);}break;
                   case 2:{strcpy(label,word3);strcpy(opcode,word2);strcpy(operand,word1);}break;
             }
             }
       void chk_label()
          {
             int k,dupsym=0;
            for(k=0;k<symcount;k++)
            if(!strcmp(label,mysymtab[k].symbol))
            {
                              mysymtab[k].addr=-1;
                              dupsym=1;
                              break;
                              }
         if(!dupsym)
         {
         strcpy(mysymtab[symcount].symbol,label);
         mysymtab[symcount++].addr=locctr;
         }
         }
      void chk_opcode()
      {
      int k=0,found=0;
      for(k=0;k<3;k++)
              if(!strcmp(opcode,myoptab[k].code))
              {
                            locctr+=3;
                            found=1;
                            break;      
               }
        if(!found)
        {
             if(!strcmp( opcode,"WORD")) locctr+=3;
             else if (!strcmp(opcode,"RESW"))locctr+=(3*atoi(operand));
             else if(!strcmp(opcode,"RESB"))locctr+=atoi(operand);
         }
   }
  int main()
           {
             PASS1();
             length=locctr-startaddr;
             PASS2();                        
             getch();
           }    

'''

Here is the input.txt file: '''

MYPGM START 1000
STA
LOOP1 JMP LOOP2
LDA
LOOP2 JMP LOOP1
RESB 04
LDA
STA
JMP LOOP1
END

''' While using linux please remove conio.h, getch() and use sprintf(args...) for itoa -- i did this here, you may change it when ruuning in windows.

You can find the code here: http://vishnunotes.blogspot.com/2012/10/how-to-implement-two-pass-assembler-in.html

Answer 1

the test:

while(strcmp(line,"END")!=0)

is wrong as fgets says:

fgets() [...] Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer.

you shoud test against "END\n"

confirmed by gdb:

(gdb) p line
$3 = "END\n\000OOP1\n\000OOP1\n\000\000\000"