PASS TWO OF TWO PASS ASSEMBLER

AIM:

To write a c program to perform pass 2 of two pass assembler.

ALGORITHM:

Step 1: Start the program.

Step 2: Create structure for input, symtab, optab, final table.

Step 3: In the main function, assign values for instructions.

Step 4: Get the input from the user and check if OPCODE=START then begin assembler.

Step 5: Calculate object code for input.

Step 6: Display the output in the table format.

Step 7: Stop the program.

SOURCE CODE:

/* PASS TWO OF TWO PASS ASSEMBLER */

#include<stdio.h>

#include<conio.h>

#include<string.h>

struct input

{

char label[10],opcode[10],operand[10],address[20];

}in[20];

struct optab

{

char opcode[10],mnemonics[10];

}op[20];

struct symbol

{

char address[10],label[10],value[10];

}sym[20];

struct finaltable

{

char address[10],opcode[10],operand[10];

}fin[10];

void main()

{

int i,k,o,s,f,flag,x,n,y;

clrscr();

o=1;

strcpy(op[1].mnemonics,"ADD");

strcpy(op[1].opcode,"10");

strcpy(op[2].mnemonics,"SUB");

strcpy(op[2].opcode,"20");

strcpy(op[3].mnemonics,"MUL");

strcpy(op[3].opcode,"30");

strcpy(op[4].mnemonics,"DIV");

strcpy(op[4].opcode,"40");

strcpy(op[5].mnemonics,"LDA");

strcpy(op[5].opcode,"50");

o=5;

printf("\nEnter the number of entries in the symbol table:\t");

scanf("%d",&n);

printf("\nAddress\tLabel\tValue\n");

for(s=1;s<=n;s++)

scanf("%s\t%s\t%s",sym[s].address,sym[s].label,sym[s].value);

i=1;

s=1;k=1;

printf("\nEnter the address:");

scanf("%s",in[i].address);

printf("\nEnter the label:");

scanf("%s",in[i].label);

printf("\nEnter the opcode:");

scanf("%s",in[i].opcode);

printf("\nEnter the operand:");

scanf("%s",in[i].operand);

while(strcmp(in[i].opcode,"END")!=0)

{

f=0;

flag=0;

for(x=1;x<=o;x++)

{

if(strcmp(in[i].opcode,op[x].mnemonics)==0)

{

flag=1;

break;

}

}

if(flag==1)

{

strcpy(fin[k].opcode,op[x].opcode);

strcpy(fin[k].address,in[i].address);

for(y=1;y<=n;y++)

{

if(strcmp(in[i].operand,sym[y].label)==0)

{

f=1;

break;

}

else

{

f=0;

}

}

if(f==1)

strcat(fin[k].operand,sym[y].address);

else if(f==0)

printf("\nSymbol Table Entry is Wong");

}

else if(strcmp(in[i].opcode,"WORD")==0||strcmp(in[i].opcode,"BYTE")==0)

strcpy(fin[k].opcode,in[i].operand);

else if(strcmp(in[i].opcode,"RESW")==0||strcmp(in[i].opcode,"RESB")==0)

strcpy(fin[k].opcode,"");

strcpy(fin[k].address,in[i].address);

i++;

k++;

printf("\nEnter the address:");

scanf("%s",in[i].address);

printf("\nEnter the label:");

scanf("%s",in[i].label);

printf("\nEnter the opcode:");

scanf("%s",in[i].opcode);

printf("\nEnter the operand:");

scanf("%s",in[i].operand);

}

printf("\n\nInput Program");

printf("\nADDRESS\tLABEL\tOPCODE\tOPERAND");

for(f=1;f<=i;f++)

printf("\n%s\t%s\t%s\t%s",in[f].address,in[f].label,in[i].opcode,in[f].operand);

printf("\nSYMBOL TABLE");

printf("\nLABEL\tADDRESS\tVALUE");

for(f=1;f<=n;f++)

printf("\n%s\t%s\t%s",sym[f].label,sym[f].address,sym[f].value);

printf("\n\nFINAL TABLE");

printf("\nADDRESS\tOBJECTCODE");

for(f=1;f<=k;f++)

{

printf("\n%s\t%s%s",fin[f].address,fin[f].opcode,fin[f].operand);

}

getch();

}

OUTPUT:

Enter the number of entries in the symbol table:        2

Address Label   Value

1006    ONE     1

1009    TWO     2

Enter the address:1000

Enter the label:COPY

Enter the opcode:START

Enter the operand:1000

Enter the address:1000

Enter the label:-

Enter the opcode:ADD

Enter the operand:ONE

Enter the address:1003

Enter the label:-

Enter the opcode:ADD

Enter the operand:TWO

Enter the address:1006

Enter the label:ONE

Enter the opcode:WORD

Enter the operand:1

Enter the address:1009

Enter the label:TWO

Enter the opcode:WORD

Enter the operand:2

Enter the address:-

Enter the label:-

Enter the opcode:END

Enter the operand:-

Input Program

ADDRESS LABEL   OPCODE  OPERAND

1000    COPY    END     1000

1000    -       END     ONE

1003    -       END     TWO

1006    ONE     END     1

1009    TWO     END     2

-       -       END     -

SYMBOL TABLE

LABEL   ADDRESS VALUE

ONE     1006    1

TWO     1009    2

FINAL TABLE

ADDRESS OBJECTCODE

1000

1000    101006

1003    101009

1006    1

1009    2

Result

Thus above program executed and output verified.