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Data Types

After learning values are, it’s likely that you have already chosen a programming language.

Most general-purpose programming languages share a small set of common basic data types.

General-Purpose

If you choose a programming language that’s attractive to beginners, they are most definitely general-purpose. Domain-specific language (DSL) is another type of programming language. These languages cannot build any type of software (yes, even JavaScript, a general-purpose language can build an operating system that’s extremely inefficient).

An example DSL is CMake which is used to configure build files that create commands to compile code to binaries and link them to become an executable.

Your first language could be dynamically-typed where every variable’s type must be specified. For dynamically-typed languages, you still need to know the type of every single value you’re looking at in your code.

message = "hello"
# Variable message points to a value whose data type is a string.

char message[] = "hello";
// Variable message holds a value whose data type is an array of characters (string).

Basic Data Types

This page will detail out 3-4 very common basic data types. Another familiar term for basic data type is called a primitive data type though across languages whether something is a primitive data type varies.

Primitive In C/C++ vs. Python

People might consider the data type string as a primitive data type in Python. In C/C++ we atomize this down further more down to characters (we don’t have an explicit type called character in Python).

Here’s an example of how strings can be regarded as “primitive” in Python but not in C/C++.

char a[] = "I'm an array of characters";

a = "I'm a string but my individual character are still 'strings'"

Numbers

A computer is able to handle different types of numbers. Any general-purpose programming language should be able to handle integers and decimals. In an unmanaged language, there are data types available depending on how much memory is needed to be reserved for a certain number.

Unmanaged Languages

Examples of unmanaged language include C/C++, Rust… These languages require you to manage memory yourself. They are often statically-typed.

Integers

I would define these as non-decimal numbers. A typical integer can represent negative numbers as well. If an unmanaged language you can have different data types that can represent a varying ranges of numbers.

In C++, a standard int takes up about 4 bytes (32 bits) of memory. The range of numbers the int data type can represent is

What if you want to only have positive numbers? Well, you can use unsigned int in an unmanaged language like C/C++. First you don’t need to reserve a bit that says whether a number is positive or negative. Second, the highest positive number you can now represent is twice that of the int. The maximum range of values are now

Decimals

Decimal numbers are defined as numbers that have a fractional part behind it. In the United States we are part of the majority that use the dot as our separator between the whole and fractional part.

Ten-Thousand Comma/Dot Two-Hundred and Six

Dot or Comma? (TRIVIA)

In much of European countries and their former colonies (e.g. Vietnam and France), , is used as the separator between whole and fractional part while . is used as the separator between different orders of whole numbers.

In 1958, during the creation of the programming language ALGOL, there was a heavy dispute regarding the type of decimal system that must be used. The programming language releases accounted for regional difference in the number system. This was famous historical deadlock where neither side of the ALGOL committee (Americans vs. Europeans) yielded.

Nowadays most standard programming language uses the period decimal.

In C/C++, the two most utilized data types for decimal numbers are double and float.

• Float vs. Double

  The basic idea is that a float represents decimal numbers but a float can represent decimal numbers that are twice as big. The more digits the a number has (more so the fractional part), the more memory is needed to represent the number.

  Data Type Names Can Vary

  This distinction is not absolute for all programming languages. For example in Python, the data type float is implemented as a double in size.

Characters and Strings

Unmanaged languages most likely have the data type for a single character, usually called char. Computers are dumb so they don’t really understand any other symbols than binary representations of numbers.

In an unmanaged language like C/C++ or Rust, you are able to see that the data type char actually only stores number. The char becomes a number when a compiler is tasked to read from the translation unit and convert the character to a number according to the ASCII chart.

Translation Unit

In an unmanaged language, a translation unit is the collection of source code packaged together and processed by the compiler. In C/C++ this can be a single source file. For Rust, its fundamental translation unit is a crate.

// These two lines of code are valid.
char a = 'a';
char b = 98;

What about a string? A string is simply a sequence/array/collection of characters. most all managed data-type include a built-in data type for string.

Booleans

This allows you to express a binary (yes/no) decision. Boolean data-types can be bool, boolean…

Like characters, internally booleans are numbers. In C, a bool is true when it holds the number 0 for false and 1 or any non-zero number for true.

bool no = false;
bool no2 = 0;
bool yes = true;
bool yes2 = 1;
bool yes3 = 123;

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Debrief

This quiz checks your understanding of basic data types, including integers, floating-point numbers, characters, strings, and booleans.

1. What is the main purpose of a data type?

A. To categorize different kinds of values B. To give every variable a unique name C. To determine which operating system runs the program D. To determine how long a program is

2. Which of the following are common basic data types? (Mark all that apply.)

A. Boolean B. Integer C. String D. Window

3. Which value is an integer?

A. 3.14 B. "17" C. -17 D. true

4. Which value would normally require a floating-point data type?

A. 42 B. 12.75 C. "12.75" D. false

5. What is the most important difference between a signed and unsigned integer?

A. Unsigned integers cannot represent negative numbers B. Signed integers cannot represent positive numbers C. Unsigned integers can only contain 0 or 1 D. Signed integers always require twice as much memory

6. A 32-bit unsigned integer can represent approximately what maximum value?

A. 255 B. 65 thousand C. 2 billion D. 4 billion

7. Which statements about floating-point numbers are true? (Mark all that apply.)

A. They can represent values with fractional parts B. A double normally provides more precision than a float in C/C++ C. They can only represent positive numbers D. Different languages may use the names float and double differently

8. Consider the following C++ code.

char letter = 'A';

What kind of value is letter intended to represent?

A. Integer B. Character C. String D. Boolean

9. Why can this C++ code be valid?

char letter = 65;

A. Characters are associated with numeric character codes B. Every integer is automatically a string C. 65 is literally stored as the letter A in the source file D. C++ ignores the assigned number

10. What best describes a string?

A. A single character B. A sequence of characters C. A number with a fractional part D. A true-or-false value

11. Which of the following are strings in Python? (Mark all that apply.)

a = "hello"
b = "A"
c = 42
d = "42"

A. a B. b C. c D. d

12. Consider these two Python values.

a = 42
b = "42"

What is the difference between them?

A. There is no difference B. a is an integer while b is a string C. a is a string while b is an integer D. Both are floating-point numbers

13. A game needs to store how many lives the player has remaining. Which type is most appropriate?

A. Boolean B. Integer C. String D. Character

14. A game needs to store whether a door is currently locked. Which type is most appropriate?

A. Boolean B. Integer C. String D. Floating-point number

15. Which of the following situations would most naturally use a Boolean? (Mark all that apply.)

A. Whether the player is alive B. The player’s username C. Whether an enemy has detected the player D. The player’s exact position on the map

16. What kind of information does a Boolean primarily represent?

A. A sequence of characters B. A whole number C. A binary condition D. A decimal number

17. Consider the following C++ code.

bool value = 123;

What will value become when 123 is converted to a Boolean? A. false B. true C. "123" D. The program must fail to compile

18. Which statement about data types across programming languages is most accurate?

A. Every programming language has exactly the same types B. Type names and implementations can differ between languages C. Only statically-typed languages have data types D. Only compiled languages have data types

19. Why do data types still matter in a dynamically-typed language such as Python?

A. Variables must explicitly declare their type B. Values still have types even when the variable does not specify one C. Python does not actually have data types D. Types only matter when the program is compiled

value = 10

20. Which statement best summarizes the relationship between values and data types?

A. Data types categorize different kinds of values B. Values categorize different kinds of variables C. Every value must be a string D. Values only have types in C/C++

Related

• Data types are how you categorize different kinds of values.
• You should also check out variables.