Additional programming techniques: The use of basic string manipulation

The idea

Strings are sequences of characters, and basic string manipulation means extracting, combining, measuring and altering text. Common operations include finding length with len("Hello") giving 5, joining strings with concatenation such as "Hello" + " " + "World", extracting a substring by slicing, for example "Computer"[0:3] giving "Com", and converting case with upper() or lower(). You can also search for a character or substring using find() or in, replace text with replace(), and split a string into parts. Indexing usually starts at 0, so the first character is at position 0. These techniques are used to validate input, format output, search records and process user responses. When manipulating strings, remember that they are immutable: operations return a new string rather than changing the original.

What earns the marks

• Uses len() to find the number of characters in a string, e.g. len("OCR") returns 3.
• Joins strings using concatenation, e.g. forename + " " + surname, and explains that both operands must be strings.
• Extracts part of a string using slicing or substring, e.g. "Computer"[0:3] returns "Com".
• Converts case using upper() or lower(), e.g. "Yes".lower() returns "yes".
• Searches within a string using find() or in, e.g. "cat" in "catalogue" returns True.
• Replaces characters or substrings using replace(), e.g. "2024".replace("4", "5") returns "2025".
• Explains that string indexing commonly starts at 0 and that strings are immutable.

Common mistakes and how to put them right

• Using 1-based indexing when the language uses 0-based indexing.

  Put it right: Check the first character position and adjust slices accordingly.

• Trying to change a string in place, such as name[0] = "J".

  Put it right: Build a new string, e.g. "J" + name[1:].

• Concatenating a string and a number without casting, e.g. "Score.

  Put it right: Cast with str(10) first.

• Confusing len() with the last index.

  Put it right: For a string of length n, valid indices are 0 to n - 1.

Exam tips

• Trace string operations on paper, writing the value after each step and counting characters carefully.
• When asked to manipulate a string, state the operation and show the result, e.g. slice, concatenate, change case.
• Check whether the question expects a single expression or a short sequence of statements, and keep code readable.
• Use quotation marks consistently and avoid mixing single and double quotes incorrectly.