Select and use appropriate data types for a problem solution

10.1 Data Types and Records

What are Data Types?

Think of a data type as a label on a box that tells the computer what kind of information it can hold. 📦

  • Primitive types – the basic building blocks (e.g., $int$, $float$, $bool$, $char$).
  • Composite types – made up of multiple primitives (e.g., array, list, record).

Choosing the Right Type

Selecting the correct data type is like picking the right sized container for your groceries. 🚚

  1. Size matters – $int$ uses 4 bytes, $long$ uses 8 bytes. Use $int$ unless you need a very large number.
  2. Precision matters – $float$ gives ~7 decimal digits, $double$ gives ~15. Use $double$ for scientific calculations.
  3. Memory vs speed – $bool$ is tiny but sometimes stored as a byte. If you need many booleans, consider a bitset.

Records (Structs)

A record is like a multi‑sectioned suitcase where each section holds a different type of item. 🧳

  • Each field has its own type.
  • Fields are accessed by name, not by position.
  • Records can be nested – a field can itself be another record.

Data Types Cheat Sheet

Type Typical Size Example Value Use Case
$int$ 4 bytes 42 Counting items, loop counters
$float$ 4 bytes 3.14 Simple physics, graphics
$double$ 8 bytes 2.71828 Precise scientific calculations
$bool$ 1 byte (often) true / false Condition checks, flags
$char$ 1 byte 'A' Single characters, ASCII
record Variable {name:"Alice", age:23} Complex data, e.g., student profile

Example Problem: Student Record

Design a record to store a student’s name, age, GPA, and enrolled status.

  • name – $string$ (or char[])
  • age – $int$
  • GPA – $float$ or $double$
  • enrolled – $bool$
In pseudocode: 
record Student {
    string name;
    int    age;
    double GPA;
    bool   enrolled;
}

Practice Questions

  1. Which data type would you use to store a student’s ID that never exceeds 9999? Explain.
  2. Design a record for a Book with fields: title, author, pages, and isHardcover.
  3. Why might you choose $double$ over $float$ for a scientific simulation?
  4. Convert the following array into a record: ["John", 30, 3.8, true] with appropriate field names.

Key Takeaways

  • Pick the smallest type that can hold your data to save memory.
  • Use record when you need to bundle related data together.
  • Remember that the choice of type can affect performance and precision.
  • Always consider future growth – choose a type that can accommodate larger values if needed.

Revision

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