List Keywords You Can't Use as Variable or Constant Names

Some words are reserved by C++, and you can't use them as variable names or constant names. These keywords have special meaning to the C++ compiler.
asm      else          new                       this
auto     enum        operator                throw
bool     explicit     private                   true
break   export      protected               try
case     extern       public                    typedef
catch    false         register                  typeid
char     float          reinterpret_cast     typename
class    for            return                    union
const   friend        short                     unsigned
goto    signed       const_cast             using
 if        sizeof        virtual                    continue
void    default       inline                     static 
delete  int             static_cast             volatile
do       long          struct                     wchar_t
double mutable    switch                    while
dynamic_cast       namespace            template

Examples: How to use variables in C++

Example 1: Integer Variables
Syntax: int variable;       //comment

#include <iostream>
using namespace std;
int term;  // term used in two expressions
int main(){
term = 4 * 7; 
cout <<"Twice " << term << " is "<< 2*term <<endl; 
cout <<"Three times " << term << " is " << 3*term <<endl; 
return 0;
}

Example 2: Floating Point Variables
Syntax:  float variable;     //comment

#include <iostream>
#include <conio.h>
using namespace std;
int i;    // an integer variable
float f; // a floating point number 
int main(){
f = 1.0 / 2.0;          // assign floating 0.5 
cout<<" f= "<<f<<endl;
i = 1 / 3;              // assign integer 0 
cout<<" i= "<<i<<endl;
f = (1 / 2) + (1 / 2);  // assign floating 0.0 
cout<<" f= "<<f<<endl;
f = 3.0 / 2.0;          // assign floating 1.5 
cout<<" f= "<<f<<endl;
i = f;                  // assign integer 1 
cout<<" i= "<<i<<endl;
return 0;
}

Example 3: Characters Variables
Syntax:  char variable;   //comment

#include <iostream>
#include <conio.h>
using namespace std;
char c1;  // first character 
char c2;  // second character 
char c3;  // third character 
int main(){
c1 = 'X'; 
c2 = 'Y'; 
c3 = 'Z'; 
cout << c1 << c2 << c3 << " reversed is "<<c3 << c2 << c1 << "\n";
return 0;
}

Variable and Using Variable in C++

Declaring Variables to Access and Use Memory
When programming in languages like C++, you define variables to store those values. Defining a variable is quite simple and follows this pattern:
       variable_type variable_name;
               or
       variable_type variable_name = initial_value;

Example:
     int i;   // variable_type: int;  variable_name: i;
     float x=1.25;  //variable_type: float;  variable_name: x; initial_value: 1.25

Declaring and Initializing Multiple Variables of a Type
You could condense the declaration of these multiple variables to one line of code that would

look like this:

Variable Types in C++:

Using Type bool to Store Boolean Values
A sample declaration of an initialized Boolean variable is
     bool male = true;
An expression that evaluates to a Boolean type is

     bool shopping = (UserSelection == “no”);

Using Type char to Store Character Values
     char User_Input = 'A';     // initialized char to ‘A’

Using Type short, int, long to Store Signed Integer Values
     short Age = 22;
     int Number = -70000;
     long LargeNumber = -70000;    //on some platforms, long is an int

     
Using Type float, double to Store Floating-Point Values
     float PI=3.14;
     double x=a/b;