C++ Fundamental Datatypes

reading

Fundamental types from cppreference.com

Data is stored in computer memory. We’ll refer to the data in memory as an object.

We can access this data:

• directly: using a descriptive object name

• indirectly: using a pointer or a reference to the memory location

Data stored in the object can be:

• mutable : we can change it—these are variables

• immutable : it cannot be changed—these are constants

There are several basic types of data:

• bool : a 1-bit true or false

• char : a 1 byte character (like 'a')

• int : an integer

• float : a single precision floating point number

• double : a double precision floating point number

Note

A floating point number is any number with a decimal point, like 2.0 or 1.e-20.

Generally, floating point numbers cannot be exactly represented on a computer, since there are infinite numbers on the number line between \([0, 1]\), but the computer only has a finite amount of memory.

Single and double precision refer to how much memory (and therefore how much precision) is used to store the numbers. Usually single precision uses 32 bits and double precision uses 64 bits. More on this later…

There are also modifiers that can be used with many of these like: short, unsigned, long.

A table of C++ datatypes is provided in the CPlusPlus tutorial variables section

Defining and Initialization

We can define a variable as:

int i;
float x;
double slope;

This tells the computer how much memory it needs to reserve for each of these objects.

Tip

C++ variable names are case-sensitive, so x and X are distinct.

Warning

Variable names can include letters, numbers, and _, but cannot begin with a number. Additionally, there are some reserved keywords (like int) that cannot be used as variable names.

Danger

It is always a good idea to initialize a variable with a starting value. Otherwise, most compilers will leave it undefined and you can run into problems if you try to use it without first remembering to initialize it.

There are a few ways to initialize. Here are the two we’ll see the most:

int i = 0;
double x{};

Both of these will initialize the variable to 0. The {} notation is more flexible, since it will work with more complicated objects that we will encounter later.

We’ll see a third way to initialize objects when we look at classes (and constructors).

Caution

Consider the following code:

#include <iostream>

int main() {

    double x;

    double y = 10;

    std::cout << x + y << std::endl;

}

Here we are using x without initializing it. This behavior is undefined, and can lead to errors that can be hard to track down.

const

Objects defined with const cannot be changed, so you are required to initialize the immediately:

const double G = 6.67e-8;

Try it…

Let’s write an example using a const variable and try to modify it.

What happens?