String/type Conversion Revision Notes for AQA GCSE Computer Science

String/type conversion

What is type conversion?

Type conversion, also known as casting, is the process of changing data from one data type to another. This is essential in programming because different operations require specific data types to work properly.

String conversion specifically refers to converting data between strings and other data types (like numbers). This is particularly important because:

User input is often received as strings
Mathematical calculations require numeric data types
Display output often needs to be in string format

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Think of it like translating between languages - you need to convert information from one format that a computer can understand to another format that's suitable for your specific task.

AQA pseudocode conversion functions

In your GCSE Computer Science exam, you'll need to know these specific AQA pseudocode functions for type conversion:

These functions work in a straightforward way:

STRING_TO_INT() - Takes a string containing numbers and converts it to an integer
STRING_TO_REAL() - Takes a string containing numbers and converts it to a real (decimal) number
INT_TO_STRING() - Takes an integer and converts it to a string
REAL_TO_STRING() - Takes a real number and converts it to a string

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Worked Example: AQA Pseudocode Conversions

# Converting strings to numbers
age ← STRING_TO_INT("16")          # age now contains integer 16
price ← STRING_TO_REAL("12.99")    # price now contains real 12.99

# Converting numbers to strings  
score ← INT_TO_STRING(85)          # score now contains string "85"
average ← REAL_TO_STRING(7.5)      # average now contains string "7.5"

Real programming languages

Different programming languages have their own syntax for type conversion, but they all achieve the same goal.

Python conversion functions

Python uses simple, memorable function names:

int(x) converts to integer
str(x) converts to string
float(x) converts to real/floating-point number

VB.Net conversion functions

VB.Net uses functions starting with 'C' (for Convert):

CInt(x) converts to integer
CStr(x) converts to string
CSng(x) converts to single-precision real number

C# conversion functions

C# uses the Convert class with descriptive method names:

Convert.ToInt32(x) converts to integer
Convert.ToString(x) converts to string
Convert.ToSingle(x) converts to real number

Common errors and limitations

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Critical Warning: Not all values can be successfully converted between data types. For example, trying to convert the string "hello" to an integer will cause an error because there's no logical way to turn text letters into a number.

Here's what happens when you try an impossible conversion in Python:

newval = int("hello")

This produces an error message like:

ValueError: invalid literal for int() with base 10: 'hello'

Exam tips

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Key Exam Strategy Points:

Learn the AQA pseudocode functions - These are exactly what you'll need in your exam
Remember the direction - "STRING_TO_" functions convert FROM strings, while "_TO_STRING" functions convert TO strings
Think about data types - Only convert values that make sense (numbers can become strings, but random text can't become numbers)
Practice with examples - Try converting between different data types in your head
Watch for trick questions - Exam questions might ask what happens when impossible conversions are attempted

Remember!

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Essential Points to Remember:

Type conversion (casting) changes data from one data type to another
AQA pseudocode uses functions like STRING_TO_INT() and INT_TO_STRING()
Real programming languages have similar functions but with different syntax (int(), CInt(), Convert.ToInt32())
Not all conversions are possible - you can't convert meaningless text like "hello" into a number
Direction matters - STRING_TO_INT converts FROM string TO integer, while INT_TO_STRING does the opposite

String/type Conversion (AQA GCSE Computer Science): Revision Notes