Variables, constants and assignment

Overview

Variables, constants and declaration, assignment with the arrow, tracing a few lines of assignments, the difference between ← and =, and choosing meaningful identifier names.

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 variable?

   Model answer

   A variable is a named location in memory that stores a value. The value can change while the program runs.

2. 2

   What is a constant?

   Model answer

   A constant is a named value that cannot change while the program runs. An example is constant PI ← 3.142.

3. 3

   What does declaring a variable do?

   Model answer

   A variable declaration creates a variable and gives it a name. Many languages also fix its data type at this point.

4. 4

   Why are named constants used?

   Model answer

   A named constant makes code easier to read, because its name explains what the value means. The value only has to be changed in one place if it ever needs updating.

5. 5

   Why is a named constant safer than typing the same value throughout a program?

   Model answer

   A constant cannot be changed by mistake while the program runs. The risk of mistyping the value in one of many places is also removed.

6. 6

   What is assignment?

   Model answer

   Assignment stores a value in a variable, replacing any value it held before. In pseudo-code assignment is written with an arrow, as in score ← 0.

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