---
title: "Address-format code for Y=(A-B/C)*[D+(E*G)]"
subject: "Computer Organization and Architecture"
chapter: 2
key: "semester_5/computer_organization_and_architecture:address-code-12"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/address-code-12
site: BCT Engineering
---

# Address-format code for Y=(A-B/C)*[D+(E*G)]

Computer Organization and Architecture · Chapter 2: Central Processing Unit

- Asked in: 2076 Chaitra, 8 marks
- Video: [Instruction Format | zero, one, two and three address instructions program | CAO | COA](https://www.youtube.com/watch?v=Htw_NTvj1ss) — Techno Tutorials ( e-Learning)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/address-code-12
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_organization_and_architecture/chapter-2

## Question

Write codes using 3, 2, 1 and 0 address instruction formats to perform the operation Y = (A - B/C)*[D+(E*G)].

## Short answer

Y = (A-B/C)*(D+E*G) needs five three-address, ten two-address, eleven one-address, and twelve zero-address instructions. The zero-address form uses a stack and directly matches the postfix expression.

## Answer

Assumptions: the operands are memory locations, `R1, R2, ...` are CPU registers, `T1, T2, ...` are temporary memory locations, and `Y` receives the result. Multiplication and division are done before addition and subtraction, and equal-priority operators go left to right.

Fully bracketed: **Y = (A-(B/C))*(D+(E*G))**. Postfix (reverse Polish) form: `A B C / - D E G * + *`.

#### Three-address instructions (OP dest, src1, src2)
```text
DIV R1, B, C   ; R1 = B / C
SUB R2, A, R1  ; R2 = A - R1
MUL R3, E, G   ; R3 = E * G
ADD R4, D, R3  ; R4 = D + R3
MUL Y, R2, R4  ; Y = R2 * R4
```
Number of instructions: 5. Shortest program, but each instruction is long (three addresses).

#### Two-address instructions (OP dest, src; dest = dest OP src)
```text
MOV R1, A   ; R1 = A
MOV R2, B   ; R2 = B
DIV R2, C   ; R2 = R2 / C
SUB R1, R2  ; R1 = R1 - R2
MOV R2, D   ; R2 = D
MOV R3, E   ; R3 = E
MUL R3, G   ; R3 = R3 * G
ADD R2, R3  ; R2 = R2 + R3
MUL R1, R2  ; R1 = R1 * R2
MOV Y, R1   ; Y = R1
```
Number of instructions: 10. A MOV is needed first because the destination operand is overwritten.

#### One-address instructions (accumulator AC is the implied operand)
```text
LOAD B    ; AC = B
DIV C     ; AC = AC / C
STORE T1  ; T1 = AC
LOAD A    ; AC = A
SUB T1    ; AC = AC - T1
STORE T2  ; T2 = AC
LOAD E    ; AC = E
MUL G     ; AC = AC * G
ADD D     ; AC = AC + D
MUL T2    ; AC = AC * T2
STORE Y   ; Y = AC
```
Number of instructions: 11. Intermediate results that cannot stay in AC are saved in memory temporaries.

#### Zero-address instructions (stack machine)
```text
PUSH A  ; push A
PUSH B  ; push B
PUSH C  ; push C
DIV     ; pop two, compute, push result
SUB     ; pop two, compute, push result
PUSH D  ; push D
PUSH E  ; push E
PUSH G  ; push G
MUL     ; pop two, compute, push result
ADD     ; pop two, compute, push result
MUL     ; pop two, compute, push result
POP Y   ; Y = top of stack
```
Number of instructions: 12. Only PUSH and POP carry an address; ADD, SUB, MUL, DIV work on the top two stack items, so the program follows the postfix form directly.

**Summary:** 3-address = 5, 2-address = 10, 1-address = 11, 0-address = 12 instructions. Fewer addresses per instruction means shorter instructions but more of them.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In Y = (A - B/C)*[D+(E*G)], which operation is done first in the first bracket?
   A. A-B
   B. A*D
   C. C*D
   D. B/C
   Answer: D. Division has priority over subtraction, so B/C comes first. (Key point: Order of evaluation)

2. What is the postfix form of the expression?
   A. A B C / - D E G * + *
   B. A B C / - D E G * + / *
   C. A B - C / D E G * + *
   D. A B C / - D E + G * *
   Answer: A. A B C / - and D E G * + are formed separately and multiplied. (Key point: Postfix form)

3. How many three-address instructions are required?
   A. 4
   B. 5
   C. 6
   D. 10
   Answer: B. Five operators (/, -, *, +, *) give five instructions. (Key point: Three-address count)

4. How many two-address instructions does the answer use?
   A. 5
   B. 8
   C. 10
   D. 12
   Answer: C. Four MOVs load operands, five arithmetic instructions compute, and the final MOV stores Y, so the total is 10. (Key point: Two-address count)

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