Answers

F6.5 Languages and translators

Robust programs · GCSE · OCR J277 2.5.1, AQA 8525 3.4.4, Edexcel 1CP2 3.3.1 · about 20 min

What this lesson is about

High and low level, machine code and assembly; compilers, interpreters and assemblers.

• High level and low level
• Assembly language
• Translators
• Which does BugBot use?
• An interpreter of your own

Questions 6 marks in all

1. [1 mark]Why must a Python program be translated before it runs?

   1. AA processor only understands its own machine code
   2. BPython is too slow
   3. CTo remove comments
   4. DTo check spelling
   Answer: A. High-level code has to become machine code, either all at once or a statement at a time.

2. [1 mark]Which translator turns assembly language into machine code?

   1. AAn assembler
   2. BA compiler
   3. CAn interpreter
   4. DAn IDE
   Answer: A. An assembler translates each assembly instruction into one machine code instruction.

3. [1 mark]Which translator produces a standalone file that runs without it?

   1. AA compiler
   2. BAn interpreter
   3. CAn editor
   4. DA debugger
   Answer: A. A compiler translates the whole program in one go into an executable file.

4. [1 mark]Why is an interpreter useful while developing a program?

   1. AIt stops at the first error, on the line where it happened
   2. BIt makes the finished program run fastest
   3. CIt produces an executable file
   4. DIt hides the source code
   Answer: A. Translating and running a line at a time makes errors easy to find and fix.

5. [1 mark]Which are features of low-level languages?

   Tick every answer that is true.

   1. AOne instruction for each processor instruction
   2. BWritten for a particular kind of processor
   3. CClose control of memory and hardware
   4. DEasy to read and move between computers
   Answer: A, B, C. Portability and readability are advantages of high-level languages.

6. [1 mark]The robot assembly program is LOAD 4, FWD 20, TURN 90, BEEP 660, DEC, JNZ 1, HALT. How many beeps does it play?

   Answer: 4. R starts at 4; each time round DEC takes one off, and JNZ jumps back until R is 0.

The task: robot assembly

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

program = ["LOAD 4", "FWD 20", "TURN 90", "BEEP 660", "DEC", "JNZ 1", "HALT"]

pc = 0
while True:
    op, *args = program[pc].split()
    if op == "FWD":
        forward(60, distance=int(args[0]))
    elif op == "TURN":
        turn_right(30, angle=int(args[0]))
    elif op == "HALT":
        break
    pc = pc + 1

from bugbot import *
connect()
program = ["LOAD 4", "FWD 20", "TURN 90", "BEEP 660", "DEC", "JNZ 1", "HALT"]

pc = 0
r = 0
while True:
    op, *args = program[pc].split()
    if op == "LOAD":
        r = int(args[0])
    elif op == "FWD":
        forward(60, distance=int(args[0]))
    elif op == "TURN":
        turn_right(30, angle=int(args[0]))
    elif op == "BEEP":
        tone(int(args[0]), 0.2)
    elif op == "DEC":
        r = r - 1
    elif op == "JNZ":
        if r != 0:
            pc = int(args[0])
            continue
    elif op == "HALT":
        break
    pc = pc + 1