Input, output, string handling and random numbers

Overview

USERINPUT and OUTPUT, LEN, POSITION and SUBSTRING, concatenation, character codes, converting between strings and numbers, and generating random whole numbers with RANDOM_INT.

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

   How does a program obtain input from the keyboard in AQA pseudo-code?

   Model answer

   The keyword USERINPUT reads a value typed at the keyboard. In name ← USERINPUT, the typed value is stored in name.

2. 2

   How does a program display data on the screen?

   Model answer

   The OUTPUT statement displays data on the screen, as in OUTPUT 'Hello'. A single OUTPUT can display text joined to the values of variables.

3. 3

   Why must keyboard input often be converted before it is used in arithmetic?

   Model answer

   Most languages read keyboard input as a string. A typed number must be converted to an integer or a real before it can be used in a calculation.

4. 4

   What does LEN('keyboard') return?

   Model answer

   The call LEN('keyboard') returns 8. The length is the number of characters in the string.

5. 5

   What does POSITION('keyboard', 'b') return in AQA pseudo-code?

   Model answer

   The call returns 3. Positions are counted from 0, so 'b' as the fourth character is at position 3.

6. 6

   What does SUBSTRING(3, 5, 'keyboard') return in AQA pseudo-code?

   Model answer

   The call returns 'boa'. The characters from position 3 to position 5 are taken, counting from 0 and including both ends.

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