String handling operations in a programming language: string to real

The idea

Converting a string to a real means taking text that holds a decimal number, such as the input "3.75", and turning it into a floating-point value the program can calculate with. Input read from the keyboard usually arrives as a string, so arithmetic on it fails until conversion happens. The learner should recognise the operation, choose the correct target type (real, not integer, because a fractional part must survive), and predict the result. For example, converting "12.5" gives the real 12.5, which can then be multiplied. Converting "12.5" to an integer would lose the .5, so the target type matters. A value that is not numeric, such as "twelve", cannot be converted and would cause an error.

What earns the marks

• Identifies that string-to-real conversion changes a text value holding a decimal number into a floating-point (real) value.
• Recognises that keyboard input is typically received as a string and must be converted before decimal arithmetic.
• Selects real (floating-point) rather than integer as the target type when a fractional part must be preserved.
• Predicts the resulting real value for a given numeric string, e.g. "3.75" becomes 3.75.
• Recognises that a non-numeric string cannot be converted and would raise an error.

Common mistakes and how to put them right

• Choosing integer as the target type.

  Put it right: Is that a real preserves the fractional part, so "3.75" must become a real, not an integer.

• Assuming input is already numeric.

  Put it right: Is that input is normally a string and needs explicit conversion before arithmetic.

• Believing any text can be converted.

  Put it right: Is that only strings representing valid numbers convert; others cause an error.

Exam tips

• Read the question's target type carefully: real means decimal values are kept.
• Check whether the string contains a decimal point to decide between real and integer.
• Remember input is a string until converted, so state the conversion step explicitly.