Variables

Variables

In most programming languages you have the concept of variables. These are simply named objects that hold a value (more formerly refereed to as state). By manipulating a variable you manipulate the state of the object that the variable referees too.

add.cpp

void addFunction()
{
    int   x = 0;      // Declare (and initialize) a variable called "x"

    x = x + 5;        // Manipulate the variable "x".
                      // The variable "x" now holds the value "5"

    int   y = x + 3;  // Declare (and initialize) a variable called "y"
                      // This will take the value "8" by adding "+" 3
                      // to the value of "x"
}

C++ is a strongly typed language. This means that each variable has a specific type that does not change (above that type is int). The operations that can be performed on an object are dependent on the type of the object and the result of the operation can depend on the types involved. C++ has several built in types (listed below) but allows the definition of new user defined types (which will be described in a later article). The standard library provides a set of commonly used user defined types (listed below).

Built in Types

char                    // Represents a character.
bool                    // Represents a boolean true/false value.
short                   // Represents an integer of at least 16 bits
int                     // Represents an integer of at least 32 bits
long                    // Represents an integer of at least 32 bits
long long               // Represents an integer of at least 64 bits
float                   // Represents a floating point number
double                  // Represents a double precision floating point number

Standard Types

// This is a list of the most commonly used types (there are many more)
std::string             // Represents a string of characters.
std::vector<T>          // Represents a dynamically sizable array
                        //     of objects with the type 'T'
std::array<T, size>     // Represents a fixed 'size'  array
                        //     of objects with the type 'T'
std::list<T>            // Represents a list of objects with the type 'T'
std::map<Key, Value>    // Represents a dictionary of key, value pairs (index by key).
                        //     The key   has type 'Key'
                        //     The value has type 'Value'
std::set<Key>           // Represents a set of keys of type 'Key'

The list may seem a bit daunting at first, but while you are learning if you restrict yourselves to three built in types (bool, int and double) and two standard types (std::string and std::vector<T>) you will be able to solve most beginner/training problems.

The other built in types are usually used when you need larger range of values or need to save space. The additional standard type (shown above) are different types of container and provide different accesses characteristics (which will be explained later). We will cover all these types in due course.

So an example of usage of the most common types is:

variables.cpp

#include <string>
#include <vector>
#include <iostream>

int main()
{
    int                       age   = 28;
    std::string               name  = "Loki";
    double                    grade = 12.45;
    std::vector<std::string>  courseNames = { "C++", "Teaching", "Maths", "Art", "Music"};

    std::cout << "Name: " << name  << "\n";
    std::cout << "Age:  " << age   << "\n";
    std::cout << "Grade:" << grade << "\n";
    std::cout << "Course 1: " << courseNames[1] << "\n";
}