Program to implement PASS 1 of a two pass Assembler.

#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<stdlib.h>

#include<ctype.h>

struct symtab

{

            char sym[10];

            int  symadd;

};

struct symtab st[20];

void main()

{

            char opcode[10],mnemonic[3],op1[10],op2[10],label[10],code[10],ic[10];

            int locctr,start,length,symcnt=0,symid=0;

            FILE *finput,*foutput,*fsymtab,*foptab;

            clrscr();

            finput=fopen("C:/SP_Prog/SP/INPUT.txt","r");

            fsymtab=fopen("C:/SP_Prog/SP/SYMTAB.txt","w");

            foutput=fopen("C:/SP_Prog/SP/OUTPUT.txt","w");

            foptab=fopen("C:/SP_Prog/SP/OPTAB.txt","r");

            fscanf(finput,"%s%s%s%s",label,opcode,op1,op2);

             char icop1[10],icop2[10];

            if(strcmp(opcode,"START")==0)

            {

                        start=atoi(op1);

                        locctr=start;

                        strcpy(icop1,"(C,");

                        strcat(icop1,op1);

                        strcat(icop1,")");

                        fprintf(foutput,"%s\t\t%s\t\t%s\n","(AD-01)",icop1,"");

                        fscanf(finput,"%s%s%s%s",label,opcode,op1,op2);

            }

            else

            locctr=0;

            int i;

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

            {

                        if(strcmp(opcode,"ORIGIN")==0)

                        {

                                    locctr=atoi(op1);

                                    strcpy(ic,"(AD,03)");

                        }

                        if(strcmp(label,"**")!=0)

                        {

                                    symcnt=symcnt + 1;

                                    if(strcmp(opcode,"EQU")==0)

                                    {

                                                if(isdigit(op1[0]));

                                                {

                                                            fprintf(fsymtab,"%s\t%d\n",label,locctr);

                                                }

                                    }

                                    symid=symid+1;

                                    fprintf(fsymtab,"%d\t\t%s\t\t%d\n",symid,label,locctr);

                          }

                        rewind(foptab);

                        fscanf(foptab,"%s%s",code,ic);

                        while(strcmp(code,NULL)!=0)

                        {

                                    if(strcmp(opcode,code)==0)

                                    {

                                                locctr+=1;

                                                break;

                                    }

                                    fscanf(foptab,"%s%s",code,ic);

                        }

                        char icop1[5];

                        if(isdigit(op1[0])!=0)

                        {

                                    strcpy(icop1,"(C,");

                                    strcat(icop1,op1);

                                    strcat(icop1,")");

                        }

                        else if(strcmp(op1,"AREG")==0)

                        {

                                    strcpy(icop1,"(1)");

                        }

                        else if(strcmp(op1,"BREG")==0)

                        {

                                    strcpy(icop1,"(2)");

                        }

                        else if(strcmp(op1,"CREG")==0)

                        {

                                    strcpy(icop1,"(3)");

                        }

                        else if(strcmp(op1,"DREG")==0)

                        {

                                    strcpy(icop1,"(4)");

                        }

                        else

                        {

                                    strcpy(icop1,op1);

                        }

                        if(strcmp(op2,"**")==0)

                                    strcpy(icop2,"");

                         else

                                    strcpy(icop2,op2);

                        fprintf(foutput,"%s\t\t%s\t\t%s\n",ic,icop1,icop2);

                        fscanf(finput,"%s%s%s%s",label,opcode,op1,op2);

            }

                        fscanf(foutput,"%s%s%s%s",label,opcode,op1,op2);

            length=locctr-start;

            printf("The length of the program is %d",length);

            fclose(finput);

            fclose(fsymtab);

            fclose(foutput);

            fclose(foptab);

            getch();

}