String Manipulation

This lesson covers string manipulation techniques as required by OCR J277 Section 2.3. String manipulation is the process of examining, modifying, and extracting parts of strings. OCR requires you to know specific string operations including length, substring, upper/lower case conversion, concatenation, and ASCII conversion.

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String Basics

A string is a sequence of characters. Each character in a string has a position (index), starting from index 0.

word = "COMPUTER"
// Index: 0=C, 1=O, 2=M, 3=P, 4=U, 5=T, 6=E, 7=R

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Length

The .length property returns the number of characters in a string.

OCR Pseudocode:

word = "Hello"
print(word.length)    // Output: 5

Python:

word = "Hello"
print(len(word))    # Output: 5

Note: the length counts all characters including spaces and punctuation. "Hi there!".length = 9.

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Substring

The .substring(start, end) method extracts a portion of a string from the start index up to (but not including) the end index.

OCR Pseudocode:

word = "COMPUTER"
print(word.substring(0, 3))    // Output: COM
print(word.substring(3, 6))    // Output: PUT
print(word.substring(4, 8))    // Output: UTER

Python:

word = "COMPUTER"
print(word[0:3])    # Output: COM
print(word[3:6])    # Output: PUT
print(word[4:8])    # Output: UTER

Example	Start	End	Result	Characters Extracted
"COMPUTER".substring(0, 3)	0	3	"COM"	Indices 0, 1, 2
"COMPUTER".substring(3, 6)	3	6	"PUT"	Indices 3, 4, 5
"COMPUTER".substring(6, 8)	6	8	"ER"	Indices 6, 7

OCR Exam Tip: The .substring(start, end) method uses zero-based indexing and the end index is EXCLUSIVE (not included). This is a very common source of errors. For "HELLO".substring(1, 4), you get characters at indices 1, 2, 3 — which is "ELL", not "ELLO".

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Upper and Lower Case Conversion

OCR Pseudocode:

word = "Hello World"
print(word.upper)    // Output: HELLO WORLD
print(word.lower)    // Output: hello world

Python:

word = "Hello World"
print(word.upper())    # Output: HELLO WORLD
print(word.lower())    # Output: hello world

Common Use: Case-Insensitive Comparison

userInput = input("Enter yes or no: ")
if userInput.lower == "yes" then
    print("You chose yes")
endif

user_input = input("Enter yes or no: ")
if user_input.lower() == "yes":
    print("You chose yes")

OCR Exam Tip: In OCR pseudocode, .upper and .lower do NOT use brackets. In Python, .upper() and .lower() DO use brackets. Make sure you use the correct syntax for whichever language you are writing in.

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Concatenation