Name visibility :

Named entities, such as variables, functions, and compound typesneed to be declared before being used in programs. The point in the programwhere this declaration happens influences its visibility.

An entity declared outside any block has global scope called“Global variables” , meaning that its name is valid anywhere in the code.While an entity declared within a block, in a function or as a functionparameters has block scope, and is only visible within the specific block inwhich it is declared, but not outside it. Variables with block scope are known as“Local variables”.

For example :

int a; // global variable

void function1 (){ int b; // local variable b = 0;}

void function2 (){ a = 1; // a is a global variable b = 2; // b is a local variable but not visible as it is not

declared in this function}

• we can also call a variable as Local variable ,If we can also declare it in

the block or constructor.

void c() {

int b=2; // b is a local variable

{ // starting mark of block int c=3; // c is also a local variablecout<<c<<endl;

} // ending mark of block}

Here b can be accessed inside the block also.

• If the global variable value is changed anywhere in the program (i.e. with

out declaring it ) ,it's value will be changed.

#include<iostream> using namespace std; int b=0; // b is a global variable void c() {

cout<<"before change : "<<b<<endl; b=2; cout<<"after changed : "<<b<<endl; {

int b=3; // local variablecout<<"in block : "<<b<<endl; // sets value to inner b

}

}

int main () {

c(); cout<<"in main : "<<b<<endl;

}

Without compiling it directly in the compiler,once u check the output by ur self. Then u will get the clear idea how the values of variables will change.

• Suppose if u want two values for the same variable in the same function,

then a new concept namespace is to be used.

Here is a set of programs for u for practice.

1.

#include <iostream> using namespace std ;int main () {

int x = 1; int y = 2; {

x = 3; int y; y = 5; cout << "inner block : \n"; cout << "x : " << x << '\n'; cout << "y : " << y << '\n';

} cout << "outer block : \n"; cout << "x : " << x << '\n'; cout << "y : " << y << '\n'; return 0; }

2.

#include <iostream> using namespace std ;

int x=0;

void c(){

cout << "x : " << x << '\n'; int x=4;cout << "x : " << x << '\n';

}

int main () {

int x = 1; int y = 2; {

x = 3; int y= 5 ; cout << "x : " << x << '\n'; cout << "y : " << y << '\n';

}

c();

cout << "x : " << x << '\n'; cout << "y : " << y << '\n'; return 0;

}

3.

#include <iostream> using namespace std ;

int x=0;

void c(){

cout << "x : " << x << '\n'; x=4;cout << "x : " << x << '\n';

}

int main () {

cout << "x : " << x << '\n'; {

x = 3; int y; y = 5;

cout << "x : " << x << '\n'; cout << "y : " << y << '\n';

}

c();

cout << "x : " << x << '\n'; cout << "y : " << y << '\n'; return 0; }

4.

#include<iostream> using namespace std;

int b=0;

class s {

public: s() {

cout<<b<<endl; int b=1; cout<<b<<endl;

} };

void c() {

cout<<b<<endl; b=2; cout<<b<<endl; int a=10; {

cout<<a<< endl; int b=3; cout<<b<<endl;

}

}

int main () {

s d; // calling constructor

b=9;

c();

cout<<b<<" " <<"main"; }

5.

#include<iostream> using namespace std; int b=0; class s {

public:

s() {

cout<<b<<endl; int b; b=1; cout<<b<<endl;

} };

void d() {

int a=15; }

void e() {

b=16; }

void c(int a,int b) {

cout<<a<<endl; cout<<b<<endl;

{

int a=10; b=12;

d(); e();

cout<<a<<endl; cout<<b<<endl;

} }

int main () {

s d; c(6,7); cout<<b<<endl;

}

The answers for this programs are available in the below link :

https://drive.google.com/folderview?id=0B5NxWL3-Gw78dW1QMXlqWXdvdUk&usp=drive_web

FOR REFERENCES :

http://comsciguide.blogspot.in/2014/12/name-visibility-namedentities-such-as.html