Peter Sobieraj

In that lesson I will describe what are variables.

Numeric variable int

At the begin let speak about variable type int. That variable is a number. And that number can be changed during working of program. For example if we are creating computer game we can have variable called number_of_lifes. Let say that at begin that variable will be equal to 3, and during game it can be changed (Player can lost or can get more lifes thanks to geting high score).
program:

int number_of_lifes= 3;
cout<<"number of your lifes is "<<number_of_lifes<<endl;

out:

number of your lifes is 3

Now lets try to change that variable program:

int number_of_lifes= 3;
cout<<"number of your lifes is "<<number_of_lifes<<endl;
number_of_lifes= 5;
cout<<"number of your lifes is "<<number_of_lifes<<endl;

out:

umber of your lifes is 3
number of your lifes is 5

OK, now lets try program with few variables, and try some numeric operations:
program:

int a=1;
int b=2;
int c=3;
cout<<"c is "<<c<<endl;
c= a+b;
cout<<"c is "<<c<<endl;
c= 2*b;
cout<<"c is "<<c<<endl;

out:

c is 3
c is 3
c is 4

You can even use variable to callculate it's new value. In mathematica it have no sense, but in programing it have.
program:

int a=2;
cout<<"a is "<<a<<endl;
a= a+1;
cout<<"a is "<<a<<endl;

out:

a is 2
a is 3

Other types of variables

here is list of standard C++ variables:

size	min	max	description
bool	1B	0	1	true or false
char	1B	-128	127	character, but can be also interpretated as number
int	4B	-2147483648	2147483647	numeric variable
float	4B	-	-	Floating point number.
double	8B	-	-	Floating point number.

char is one sinlge character, and if you want to set it value you need to set it's value between ' ' (not " ").

char c= 'c';

Working example:

#include <iostream>
#include <cstdlib>
using namespace std;
 
int main()
{
    bool b= 0;
    int i= 123;
    float f=3.14;
    double d= 3.14159265358979323846;
    cout<<"b have logic value "<<b<<endl;
    cout<<"i is "<<i<<endl;
    cout<<"f approximating value is "<<f<<endl;
    cout<<"d approximating value is "<<d<<endl;
    return 0;
}

output:

b have logic value 0
i is 123
f approximating value is 3.14
d approximating value is 3.14159