← IGCSE Computer Science Paper 1

Advantages of an interpreter

Runs code line by line with no wait to compile, so unfinished programs can be tested at once. It stops at the faulty line, making errors easy to find. Source code runs on any machine with one.

Part of: IGCSE Computer Science 0478 — 4.2 Programming Languages, Translators and IDEs — Module 22

Understanding Advantages of an interpreter in IGCSE Computer Science Paper 1

What it does: The interpreter runs the lines that exist so the programmer can check them, even though the rest of the program is incomplete. The interpreter translates the source code for its own machine, so one copy of the code works on each machine that has the interpreter. An interpreter runs code line by line, so part-finished programs can be tested without translating the whole thing first. The interpreter halts at the error, so the programmer knows exactly which line to fix. Being able to test as you go is a key advantage of an interpreter during development. Interpreted programs are usually slower, so speed is not an advantage. Testing incomplete code is.

Common mistakes: The closing bracket is missing. An interpreter runs line 1 at once, then stops at line 2 and reports the error, so the faulty line is clear. It should be print('Hi ' + name). totl is a misspelt variable name. An interpreter lets you test the unfinished program straight away, and it stops at line 3 with a name error. It should be total = total + n.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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This module's key terms are also in a printable crossword (Modules 440–449) and word search (Modules 440–463).

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Learning
Duo
A student has written only the first half of a program. Which translator lets them test that half straight away?
CompilerInterpreter
Matches
Interpreter: the whole program must be compiled first, so wait before testing
↓
An interpreter does not compile the whole program first. It runs the code line by line, so there is no wait before testing.
Applying
Meanings
Term
interpreter
Meaning
Runs code line by line with no wait to compile, so unfinished programs can be tested at once. It stops at the faulty line, making errors easy to find. Source code runs on any machine with one.
Practice
// Test this part now
Testing
Gaps
add(a, b):
Check Answer
Spots
1name = input('Name? ')
2print('Hi ' + name

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Quick Questions

1. A student has written only the first half of a program. Which translator lets them test that half straight away?
A. Compiler
B. Interpreter ✓
An interpreter runs code line by line, so part-finished programs can be tested without translating the whole thing first.
2. Which statement about an interpreter is correct?
A. It must create a complete executable file before the program can run
B. There is no wait for the whole program to be compiled before it runs ✓
An interpreter translates and runs each line as it goes, so there is no compile step to wait for.
3. A program has a mistake on line 12. What does an interpreter do when it reaches that line?
A. It stops at line 12, so the faulty line is easy to find ✓
B. It skips line 12 and reports every error at the very end
The interpreter halts at the error, so the programmer knows exactly which line to fix.
4. Why is an interpreter useful when a programmer is still writing a program?
A. They can run and test unfinished code immediately ✓
B. They must finish the whole program before testing anything
Being able to test as you go is a key advantage of an interpreter during development.
5. Ali writes his source code on a Windows laptop. Zara has a Mac with the same interpreter installed. What is true?
A. The same source code can run on Zara's Mac ✓
B. Zara must wait for a new executable file made for her Mac
Source code can run on any machine that has the interpreter, so one copy works on many systems.

Match the Pairs

Interpreter: run line 1, run line 2, run line 3 → Runs the program straight away with no wait for compilation, so a programmer can test changes at once
Line 4 error -> interpreter stops at line 4 → Execution halts at the faulty line, so the programmer can see exactly where the error is
An interpreter lets you test part of a program before it is finished → print("Hello") # lines 1-2 only, rest not written yet
The same source code can run on any machine that has an interpreter → Windows + interpreter, Mac + interpreter, Linux + interpreter -> same source code
Interpreter: the whole program must be compiled first, so wait before testing → An interpreter does not compile the whole program first. It runs the code line by line, so there is no wait before testing.
Interpreter: the program cannot be tested until every line has been written → An interpreter can run an unfinished program, so part of it can be tested before the rest is written.

Key Term

interpreter
Runs code line by line with no wait to compile, so unfinished programs can be tested at once. It stops at the faulty line, making errors easy to find. Source code runs on any machine with one.

Fill in the Blanks

1. # Test this part now, the rest is unfinished def add(a, b): return a + b
Hint: Type the keyword that defines a function, so this finished part can be run and tested at once.
2. print("Line 1 runs") print(10 / 0) print("Never reached")
Hint: Type the operator for division. Dividing by zero causes an error, so the interpreter stops on this line.
3. # No compile step: run it straight away python game.py
Hint: Type the command that starts the Python interpreter so the program runs with no wait for compilation.
4. total = 5 + 3 print(total) # TODO: add the tax calculation later
Hint: Type the variable name to display, so you can test the unfinished program straight away.
5. # Run now: it stops at any faulty line age = int(input("Age: ")) print(age)
Hint: Type the function name that reads what the user types, so this part can be tested before the program is complete.

Spot the Error

Question 1
A name = input('Name? ')
B print('Hi ' + name
C print('Ready')
Line B — The closing bracket is missing. An interpreter runs line 1 at once, then stops at line 2 and reports the error, so the faulty line is clear. It should be print('Hi ' + name).
Question 2
A total = 0
B for n in range(3):
C total = totl + n
D print(total)
E # TODO: average
Line C — totl is a misspelt variable name. An interpreter lets you test the unfinished program straight away, and it stops at line 3 with a name error. It should be total = total + n.
Question 3
A x = 4
B y = 6
C prnt(x * y)
Line C — prnt is not a real function. The interpreter runs lines 1 and 2, then stops at line 3 and points to the mistake. It should be print(x * y).
Question 4
A def area(w, h)
B return w * h
C print(area(3, 4))
Line A — A function header needs a colon at the end. The interpreter stops at line 1 and reports it, so you can fix it and test again with no compile wait. It should be def area(w, h):
Question 5
A age = 15
B if age < 13:
C print('Child')
D else
E print('Teen')
Line D — else must be followed by a colon. The interpreter stops at this line, which makes the error easy to locate. It should be else:

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