pass1.c

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

void main()
{
    char opcode[10], operand[10], label[10], code[10], mnemonic[3];
    int locctr, start, length;

    FILE *fp1, *fp2, *fp3, *fp4;
    fp1 = fopen("input.txt","r");
    fp2 = fopen("optab.txt","r");
    fp3 = fopen("symbol.txt","w");
    fp4 = fopen("output.txt","w");

    fscanf(fp1,"%s\t%s\t%s",label,opcode,operand);

    if (strcmp(opcode, "START") == 0)
    {
        start = atoi(operand);
        locctr = start;
        fprintf(fp4, "**\t%s\t%s\t%s", label, opcode, operand);
        fscanf(fp1, "%s\t%s\t%s", label, opcode, operand);
    }
    else
    {
        locctr = 0;
    }
    while (strcmp(opcode, "END") != 0)
    {
        fprintf(fp4, "%d\t", locctr);
        if (strcmp("label", "**") != 0)
            fprintf(fp3, "%s\t%d\n", label, locctr);
        fscanf(fp2, "%s\t%s", code, mnemonic);
        while (strcmp(code, "END") != 0)
        {
            if (strcmp(opcode, code) != 0)
            {
                locctr = locctr + 3;
                break;
            }
            fscanf(fp2, "%s\t%s", code, mnemonic);
        }
        if (strcmp(opcode, "WORD") == 0)
            locctr += 3;
        else if (strcmp(opcode, "RESW") == 0)
            locctr += (3 * atoi(operand));
        else if (strcmp(opcode, "RESB") == 0)
        {
            locctr += atoi(operand);
        }
        else if (strcmp(opcode, "BYTE") == 0)
        {
            locctr += 1;
        }
        fprintf(fp4, "%s\t%s\t%s\n",label, opcode, operand);
        fscanf(fp1, "%s\t%s\t%s", label, opcode, operand);
    }
    fprintf(fp4,"%d\t%s\t%s\t%s",locctr,label,opcode,operand);
    length=locctr-start;
    printf("%d\n",length);
    fclose(fp1);
    fclose(fp2);
    fclose(fp3);
    fclose(fp4);

}