---
title: "Address-format code for Y=(A-B+C)*(E+F/G)"
subject: "Computer Organization and Architecture"
chapter: 2
key: "semester_5/computer_organization_and_architecture:address-code-10"
source: https://www.bctengineer.com/q/semester_5/computer_organization_and_architecture/address-code-10
site: BCT Engineering
---

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

Computer Organization and Architecture · Chapter 2: Central Processing Unit

- Asked in: 2079 Baisakh, 6 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-10
- 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)*(E+F/G).

## Short answer

For Y = (A-B+C)*(E+F/G), postfix is A B - C + E F G / + *. Three-address code uses 5 instructions (SUB, ADD, DIV, ADD, MUL). Two-address requires 9 instructions with MOVs. One-address accumulator needs 9 instructions using temporary T1. Zero-address stack machine uses 12 instructions following postfix with PUSH/POP. Three-address is most compact; zero-address has shortest instructions but most instructions overall.

## 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)*(E+(F/G))**. Postfix (reverse Polish) form: `A B - C + E F G / + *`.

#### Three-address instructions (OP dest, src1, src2)
```text
SUB R1, A, B   ; R1 = A - B
ADD R2, R1, C  ; R2 = R1 + C
DIV R3, F, G   ; R3 = F / G
ADD R4, E, R3  ; R4 = E + 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
SUB R1, B   ; R1 = R1 - B
ADD R1, C   ; R1 = R1 + C
MOV R2, E   ; R2 = E
MOV R3, F   ; R3 = F
DIV 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: 9. A MOV is needed first because the destination operand is overwritten.

#### One-address instructions (accumulator AC is the implied operand)
```text
LOAD A    ; AC = A
SUB B     ; AC = AC - B
ADD C     ; AC = AC + C
STORE T1  ; T1 = AC
LOAD F    ; AC = F
DIV G     ; AC = AC / G
ADD E     ; AC = AC + E
MUL T1    ; AC = AC * T1
STORE Y   ; Y = AC
```
Number of instructions: 9. 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
SUB     ; pop two, compute, push result
PUSH C  ; push C
ADD     ; pop two, compute, push result
PUSH E  ; push E
PUSH F  ; push F
PUSH G  ; push G
DIV     ; 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 = 9, 1-address = 9, 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. How is A-B+C in Y = (A-B+C)*(E+F/G) evaluated?
   A. As A-(B+C)
   B. As (A+C)-B
   C. As (A-B)+C, left to right
   D. As A-(B*C)
   Answer: C. Subtraction and addition have equal priority, so they go left to right. (Key point: Left-to-right rule)

2. What is the postfix form of the expression?
   A. A B C - + E F G / + *
   B. A B - C + E F G / + *
   C. A B - C + E F / G + *
   D. A B - C + E F G + / *
   Answer: B. A B - C + gives the first bracket; F G / is added to E; then *. (Key point: Postfix form)

3. How many three-address instructions are needed?
   A. 5
   B. 3
   C. 6
   D. 9
   Answer: A. Five operators (-, +, /, +, *) give five instructions. (Key point: Three-address count)

4. In one-address code, why are STORE Tn instructions needed in the middle of the program?
   A. To convert the expression to postfix form
   B. Because the ALU cannot add numbers directly
   C. To increase the number of addresses per instruction
   D. The accumulator is the only implied register, so an intermediate result must be saved in memory before AC is reused
   Answer: D. AC holds only one value; a partial result needed later has to be stored in a temporary memory location. (Key point: Temporaries in one-address code)

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- [Address-format code for X=(A-B*F)*C+D/E](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aaddress-code-6) — Computer Organization and Architecture, chapter 2, asked 16×
- [Address-format code for Y=A/B+(C×D)+F(H/G)](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aaddress-code-8) — Computer Organization and Architecture, chapter 2, asked 16×
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- [Address-format code for Y=(A-B/C)*[D+(E*G)]](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aaddress-code-12) — Computer Organization and Architecture, chapter 2, asked 16×
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- [Address-format code for Y=AB+(F/G)+CD](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aaddress-code-17) — Computer Organization and Architecture, chapter 2, asked 16×

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