Variables in C++
A variable is a name which is associated with a
value that can be changed. For example when I write int num=20; here
variable name is num which is associated with value 20, int is a data type that
represents that this variable can hold integer values. We will cover the data
types in the next tutorial. In this tutorial, we will discuss about variables.
Syntax of declaring a variable in C++
data_type variable1_name = value1, variable2_name =
value2;
For example:
int num1=20, num2=100;
We can also write it like this:
int num1,num2;
num1=20;
num2=100;
Types
of variables
Variables can be categorised
based on their data type. For example, in the above example we have seen
integer types variables. Following are the types of variables available in C++.
int: These type of of variables holds integer value.
char: holds character value like ‘c’, ‘F’, ‘B’, ‘p’, ‘q’ etc.
bool: holds boolean value true or false.
double: double-precision floating point value.
float: Single-precision floating point value.
Types
of variables based on their scope
Before going further lets
discuss what is scope first. When we discussed the Hello World Program, we
have seen the curly braces in the program like this:
int main {
//Some code
}
Any variable declared inside
these curly braces have scope limited within these curly braces, if you declare
a variable in main() function and try to use that variable outside main()
function then you will get compilation error.
Now that we have understood what is scope.
Lets move on to the types of variables based on the scope.
1. Global variable
2. Local variable
2. Local variable
Global
Variable
A variable declared outside
of any function (including main as well) is called global variable. Global
variables have their scope throughout the program, they can be accessed
anywhere in the program, in the main, in the user defined
function, anywhere.
Global variable example
Here we have a global variable
myVar, that is declared outside of main. We have
accessed the variable twice in the main() function without any issues.#include <iostream>
using namespace std;
// This is a global variable
char myVar = 'A';
int main()
{
cout <<"Value of myVar: "<< myVar<<endl;
myVar='Z';
cout <<"Value of myVar: "<< myVar;
return 0;
}
Output:
Value of myVar: A
Value of myVar: Z
Local variable
Local variables are declared inside the braces
of any user defined function, main function, loops or any control statements (if,
if-else etc.) and have their scope limited inside those braces.
Local variable
example
#include <iostream>
using namespace std;
char myFuncn() {
// This is a local variable
char myVar = 'A';
}
int main()
{
cout <<"Value of myVar: "<< myVar<<endl;
myVar='Z';
cout <<"Value of myVar: "<< myVar;
return 0;
}
Output:
Compile time error, because we are trying to access the variable
Compile time error, because we are trying to access the variable
myVar outside of its scope. The scope of myVar is limited to the body of function myFuncn(), inside those braces.
Can global
and local variable have same name in C++?
Lets see an example having same name global
and local variable.
#include <iostream>
using namespace std;
// This is a global variable
char myVar = 'A';
char myFuncn() {
// This is a local variable
char myVar = 'B';
return myVar;
}
int main()
{
cout <<"Funcn call: "<< myFuncn()<<endl;
cout <<"Value of myVar: "<< myVar<<endl;
myVar='Z';
cout <<"Funcn call: "<< myFuncn()<<endl;
cout <<"Value of myVar: "<< myVar<<endl;
return 0;
}
Output:
Funcn call: B
Value of myVar: A
Funcn call: B
Value of myVar: Z
As you can see that when I changed the value
of
myVar in the main function, it only
changed the value of global variable myVar because local variable myVar scope is limited to the function myFuncn().
