Notes:

Variables in C++ Programming Language :

What is a variable & constant?

Variable:
Variable is a named memory location, whose value can change during the execution of a program.

Constant:
Constant is a named memory location, whose value never changes during the execution of a program.

i.e. constants stay constant whereas variables vary.

W.K.T. While developing any software application using C++; we will be dealing with different types of data and data values. In order to store and process different types of data & data values computer uses its memory (RAM). To allocate a chunk of memory and access it within a program, we need to declare a variable or a constant.

Declaring a variable or a constant: means allocating a memory location for some data

Syntax for declaring a variable:
datatype nameOfVariable; // declaration of a single variable
Ex:
int playerScore;

Note: By default the value of a variable is garbage value (means a meaningless or useless value)

- Having a garbage value inside a variable is considered as one of the bad practice. So while declaring a variable; it is recommended to initialize it with some meaningful value. Initializing a variable while declaring; is considered as one of the best practice.

Initializing a variable or a constant: means assigning the initial value to that allocated memory location

Syntax for declaring and initializing a variable:
datatype nameOfVariable = value; // declaration and initialization of a single variable
Ex:
int playerScore = 0;

Syntax for declaring multiple variables:
datatype nameOfVariable1, nameOfVariable2,...; // declaration of multiple variables
Ex:
int playerScore, playerHealth;

Syntax for declaring & initializing multiple variables:
datatype nameOfVariable1 = value, nameOfVariable2 = value,…; // declaration & initialization of multiple variables
Ex:
int playerScore=0, playerHealth=100;

- In order to change the value in a variable after declaring or declaring and initializing, we need to assign a value to it.

Assigning a variable:

Syntax for assigning value to a variable:
nameOfVariable = newValue; // changing value of a variable
Ex:
playerScore = 10;
playerHealth = 80;

Note:
- In C language; all variables must be declared in the beginning of the scope
- In C++ language; variables can be declared anywhere in the scope
- Before using a variable it must and should be declared

Example Code:

#include <iostream>

using namespace std;

int main()
{
/*
int playerScore;
cout << "player score = " << playerScore << endl; // GIV

int playerHealth;
cout << "player health = " << playerHealth << endl; // GIV

int playerScore = 0;
cout << "player score = " << playerScore << endl; // 0

int playerHealth = 100;
cout << "player health = " << playerHealth << endl; // 100

int playerScore, playerHealth;
cout << "player score = " << playerScore << endl; // GIV
cout << "player health = " << playerHealth << endl; // GIV
*/

int playerScore=0, playerHealth=100;
cout << "player score = " << playerScore << endl; // 0
cout << "player health = " << playerHealth << endl; // 100

playerScore = 10;
playerHealth = 80;

cout << "player score = " << playerScore << endl; // 10
cout << "player health = " << playerHealth << endl; // 80

return 0;
}