String Manipulation

What is string manipulation?

String manipulation or string handling is the use of programming techniques to modify, analyse or extract information from a string
Examples of string manipulation include:
- Case conversion (modify)
- Length (analyse)
- Substrings (extract)
- Concatenation (modify)
- ASCII conversion (analyse)

Case conversion

The ability to change a string from one case to another, for example, lower case to upper case

Function	Pseudocode	Python	Output
Uppercase	`Name ← "Sarah"` `OUTPUT TOUPPER(Name)`	`Name = "Sarah"` `print(Name.upper())`	"SARAH"
Lowercase	`Name ← "SARAH"` `OUTPUT TOLOWER(Name)`	`Name = "SARAH"` `print(Name.lower())`	"sarah"
Title case	`Book ← "inspector calls"` `OUTPUT TOTITLE(Book)`	`Book = "inspector calls"` `print(Book.title())`	"Inspector Calls"

Length

The ability to count the number of characters in a string, for example, checking a password meets the minimum requirement of 8 characters

Function Pseudocode Python Output

Length

Password ← "letmein"

OUTPUT LEN(Password)

Password = "letmein"

print(len(Password))

Password ← "letmein"

IF LEN(Password) >= 8 then

OUTPUT "Password accepted"

ELSE

OUTPUT "Password too short"

ENDIF

Password = "letmein"

if len(Password) >= 8:

print("Password accepted")

else:

print("Password too short")

"Password too short"

Substring

The ability to extract a sequence of characters from a larger string in order to be used by another function in the program, for example, data validation or combining it with other strings
Extracting substrings is performed using 'slicing', using specific start and end to slice out the desired characters
Substring is 0 indexed (first value is 0 not 1)

Function	Pseudocode	Python	Output
Substring	substring(starting character, number of characters)	string[start character : end character]
	`Word ← "Revision"` `OUTPUT SUBSTRING(Word,2,3)`	`Word = "Revision"` `print(Word[2:5])`	"vis"
	left(number of characters)
	`Word ← "Revision"` `OUTPUT LEFT(Word,4)`	`Word = "Revision"` `print(Word[:4])`	"Revi"
	right(number of characters)
	`Word ← "Revision"` `OUTPUT RIGHT(Word,4)`	`Word = "Revision"` `print(Word[4:])`	"sion"

Concatenation

The ability to join two or more strings together to form a single string
Concatenation uses the '+' operator to join strings together

Function	Pseudocode	Python	Output
Concatenation	`FName ← "Sarah"` `SName ← "Jones"` `FullName ← FName + SName` `OUTPUT(FullName)`	`FName = "Sarah"` `SName = "Jones"` `FullName = FName + SName` `print(FullName)`	"SarahJones"
	`FName ← "Sarah"` `SName ←"Jones"` `FullName ← FName + " " + SName` `OUTPUT(FullName)`	`FName = "Sarah"` `SName = "Jones"` `FullName = FName + " " + SName` `print(FullName)`	"Sarah Jones"
	`Name ← "Sarah"` `OUTPUT("Hello, " + Name)`	`Name = "Sarah"` `print("Hello, " + Name)`	"Hello, Sarah"

ASCII conversion

The ability to return an ASCII character from a numerical value and vice versa

Function	Pseudocode	Python	Output
ASCII conversion	`CHAR_TO_CODE(A)`	`print(ord("A"))`	"65"
ASCII conversion	`CODE_TO_CHAR(97)`	`print(chr(97))`	"a"

What is casting?

Casting is when you convert one data type to another data type

Example

The following Python program is used to capture a users age to determine if they are old enough to vote

Line	Python code
01	age = input("Enter age")
02	if age >= 18:
03	print("Old enough to vote")
04	else:
05	print("Too young to vote")

In this example, on line 01, no specific data type is requested
By default the data type is stored as 'string'
On line 02, a run-time error would occur because age is stored as a string and is being compared to an integer value in the selection statement
Casting the age from a string to an integer would solve the error

Line	Python code
01	age = input("Enter age")
02	if int(age) >= 18:
03	print("Old enough to vote")
04	else:
05	print("Too young to vote")

In the corrected code, casting is highlighted in green

String Conversion Operations

Conversion	Example	Output
From String to Integer	`STRING_TO_INT ("10")`	10
From Integer to String	`INT_TO_STRING (5)`	"5"
From String to Real	`STRING_TO_REAL ("16.5)`	16.5
From Real to String	`REAL_TO_STRING (5.4)`	"5.4"

Exam Tip

Remember that the '+' operator is used for concatenation of strings BUT is also the mathematical operator for addition

It is important to remember, that the same operator symbol performs different roles on different types of data (integer/string)

Worked example

A school wants to use a program to take a students first name, last name and year of entry as inputs and use them to create a username

They want the username to follow the rule:

Initial + First 3 letters of last name + year

For example, a student named David Hamilton who started in 2024 would have the username:

DHam2024

The algorithm has been started below:

Line	Algorithm
01	`FName = input("Enter first name")`
02	`LName = input("Enter last name")`
03	`year = input("Enter year")`
04	`username =`
05	`print(username)`

Use string manipulation to complete line 04 to create the username [3]

How to answer this question

What techniques do we need to use to create the username? substring to extract the parts of the first and last name
Concatenation to join them together

Answer

Line	Algorithm
01	`FName = input("Enter first name")`
02	`LName = input("Enter last name")`
03	`year = input("Enter year")`
04	`username = FName.substring(0,1) + LName.substring(0,3) + year`
05	`print(username)`

Guidance

FName.substring(0,1) 1 mark
LName.substring(0,3) 1 mark
username = FName.substring(0,1) + LName.substring(0,3) + year 1 mark

String Manipulation (AQA GCSE Computer Science)

Revision Note