String conversion operations.

The idea

String conversion operations change a value from one data type to a string, or change a string into another type. In AQA 8525 you meet conversions such as turning an integer into text so it can be joined to other text, and turning a string of digits into an integer so arithmetic can be performed. For example, in Python str(42) gives the string "42", and int("42") gives the integer 42. A conversion does not change the characters themselves; it changes the data type the program treats the value as. Learners should recognise which operation is needed for a given task, predict the resulting type, and understand that joining text to a number usually requires converting the number first.

What earns the marks

• Identifies that a string conversion operation changes a value's data type to or from string.
• Recognises an example such as converting an integer to a string so it can be concatenated with text.
• Distinguishes conversion from concatenation: conversion changes type, concatenation joins strings.
• Predicts the data type produced by a given conversion, for example that converting a number to a string yields text.
• Explains that converting a string of digits to a number allows arithmetic to be carried out.

Common mistakes and how to put them right

• Confusing conversion with concatenation.

  Put it right: Is that conversion changes the data type while concatenation joins two strings together.

• Assuming a number stored as text can be added arithmetically without conversion.

  Put it right: Is that it must first be converted to an integer or real.

• Thinking conversion alters the characters themselves.

  Put it right: Is that the characters stay the same but the data type changes.

Exam tips

• Read the question to identify the required input and output data types before choosing an operation.
• Remember that joining text to a number usually needs the number converted to a string first.
• Check whether the task needs arithmetic (convert to number) or display/joining (convert to string).