Logic errors, test data and efficiency

Overview

Syntax, logic and runtime errors, finding and fixing logic errors in algorithms, normal, boundary and erroneous test data, and judging efficiency by compares, passes and memory.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a syntax error?

   Model answer

   A syntax error breaks the grammar rules of the programming language. The code cannot be translated and run until the error is fixed.

2. 2

   What is a logic error?

   Model answer

   A logic error lets the program run but makes it produce the wrong result. The instructions are valid but do not do what was intended.

3. 3

   Define a runtime error.

   Model answer

   A runtime error happens while the program is running and makes it crash. A division by zero is a common cause.

4. 4

   Why is a logic error harder to find than a syntax error?

   Model answer

   The translator reports a syntax error with its line number. A logic error gives no message, so it only shows when the output is checked against the expected result.

5. 5

   An algorithm should find the largest of a list of positive numbers. The algorithm sets largest to 0 and, for each number, replaces largest if number < largest. Identify and correct the error.

   Model answer

   The comparison is the wrong way round, so largest never changes from 0. The condition should be number > largest.

6. 6

   An algorithm should add up the ten items of an array indexed 0 to 9, but its loop runs from index 1 to 9. What is wrong?

   Model answer

   The item at index 0 is never added, so the total is too small. The loop should start at index 0.

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.