lesson
Input needs validation before arithmetic
1 · Learn
Python's input function returns text. Converting suitable text with int can produce an integer, but input such as 'apple' cannot become an integer through that conversion. A robust program must handle unsuitable input rather than assume every user follows the prompt.
Separate collecting input, validating it, converting it and calculating. Do not ask learners to enter real personal details for a programming exercise.
2 · Worked example
For a model quantity prompt, '12' can represent twelve items, but an empty string or 'twelve-ish' needs a clear response instead of an unhandled failure.
3 · Your turn
Why can adding 1 directly to text returned by input fail in Python?
Check your answer
The value is a string, not automatically a number; validate and convert suitable input before numerical addition.
4 · Apply your learning
Design expected responses for valid, empty, negative and non-numeric fictional quantities before implementing the prompt.
Adult guidance and safety
Use an approved private programming or authoring environment and fictional data. Do not install unknown software or enter personal credentials for these exercises. Trace first, then run and test where a suitable tool is available; these text examples do not themselves provide an executable assessment environment.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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