Sequence and selection

Overview

Nested IF, term condition and relational operators used in conditions.

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 sequence?

   Model answer

   Sequence means that instructions are carried out one after another in the order written. Each step finishes before the next begins.

2. 2

   Why does the order of a sequence matter?

   Model answer

   A later step often depends on a value produced by an earlier one. Reordering the steps can therefore give a wrong result.

3. 3

   What is selection?

   Model answer

   Selection means that a program chooses between different sets of instructions. The choice depends on whether a condition is true.

4. 4

   Write pseudo-code for a simple IF statement.

   Model answer

   The form is IF mark ≥ 40 THEN OUTPUT pass, then END IF. Only a mark of 40 or more produces the output.

5. 5

   Write pseudo-code for an IF statement with an alternative branch.

   Model answer

   The form is IF mark ≥ 40 THEN OUTPUT pass ELSE OUTPUT fail, then END IF. Exactly one of the two branches runs.

6. 6

   What is a nested IF?

   Model answer

   A nested IF places one selection inside a branch of another. The second condition is tested only when the first has been met.

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