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global and block scope
#include <iostream.h>
int n=0; //Global
main()
{
int n = 1;
{
int n = 2 ;
{
int n = 3;
cout << "In inner n=" <<n<<endl;
cout << "Global n=" << ::n <<endl;
}
cout << "In outter n=" <<n<<endl;
cout << "Global n=" <<::n<<endl;
}
cout << "In main() n=" << n<<endl;
return 0 ;
}In inner n=3
Global n=0
In outter n=2
Global n=0
In main() n=1
global variables across functions
#include <iostream>
using namespace std;
int glob = 10; // global variable
void access_global();
void hide_global();
void change_global();
int main()
{
cout << "In main() glob is: " << glob << "\n\n";
access_global();
hide_global();
cout << "In main() glob is: " << glob << "\n\n";
change_global();
cout << "In main() glob is: " << glob << "\n\n";
return 0;
}
void access_global()
{
cout << "In access_global() glob is: " << glob << "\n\n";
}
void hide_global()
{
int glob = 0; // hide global variable glob
cout << "In hide_global() glob is: " << glob << "\n\n";
}
void change_global()
{
glob = -10; // change global variable glob
cout << "In change_global() glob is: " << glob << "\n\n";
}Inner block variable scope
#include <iostream>
using namespace std;
int main()
{
int i;
int j;
i = 10;
j = 100;
if(j > 0) {
int i; // this i is separate from outer i
i = j / 2;
cout << "inner i: " << i << "\n";
}
cout << "outer i: " << i << "\n";
return 0;
}inner i: 50
outer i: 10
Names in inner scopes can hide names in outer scopes.
#include <iostream>
#include <ostream>
int main()
{
for (int i = 0; i < 10; ++i)
{
int x = 2;
if (x < i)
{
double x = 3.4;
std::cout << x;
}
std::cout << x;
}
//std::cout << x; // Error: no x declared in this scope
}2223.423.423.423.423.423.423.42
scope code block
#include <iostream>
using namespace std;
void func();
int main()
{
int var = 5;
cout << "In main() var is: " << var << "\n\n";
func();
cout << "Back in main() var is: " << var << "\n\n";
{
cout << "In main() in a new scope var is: " << var << "\n\n";
cout << "Creating new var in new scope.\n";
int var = 10;
cout << "In main() in a new scope var is: " << var << "\n\n";
}
cout << "At end of main() var is: " << var << "\n";
return 0;
}
void func()
{
int var = -5; // local variable in func()
cout << "In func() var is: " << var << "\n\n";
}Using the scope resolution operator: "::"
#include <iostream>
using std::cout;
using std::endl;
int count1 = 100;
int main() {
int count1 = 10;
int count3 = 50;
cout << endl << "Value of outer count1 = " << count1;
cout << endl << "Value of global count1 = " << ::count1;
{
int count1 = 20;
int count2 = 30;
cout << endl << "Value of inner count1 = " << count1;
cout << endl << "Value of global count1 = " << ::count1;
count3 += count2;
}
cout << endl
<< "Value of outer count1 = " << count1
<< endl
<< "Value of outer count3 = " << count3;
cout << endl;
return 0;
}Value of outer count1 = 10
Value of global count1 = 100
Value of inner count1 = 20
Value of global count1 = 100
Value of outer count1 = 10
Value of outer count3 = 80
Using the scope resolution operator (2)
#include <iostream>
#include <ostream>
namespace n {
struct counter {
static int n;
};
double n = 2.8;
}
int n::counter::n = 7;
int main()
{
int counter = 0;
int n = 10;
std::cout << n::counter::n;
std::cout << n::n;
std::cout << x.n;
std::cout << n;
std::cout << counter;
}Value of outer count1 = 10
Value of global count1 = 100
Value of inner count1 = 20
Value of global count1 = 100
Value of outer count1 = 10
Value of outer count3 = 80
Variable block scope
#include <iostream>
using std::cout;
using std::endl;
int main() {
int count1 = 10;
int count3 = 50;
cout << endl << "Value of outer count1 = " << count1;
{
int count1 = 20;
int count2 = 30;
cout << endl << "Value of inner count1 = " << count1;
count1 += 3;
count3 += count2;
}
cout << endl
<< "Value of outer count1 = " << count1
<< endl
<< "Value of outer count3 = " << count3;
cout << endl;
return 0;
}Value of outer count1 = 10
Value of inner count1 = 20
Value of outer count1 = 10
Value of outer count3 = 80
Variables can be local to a block
#include <iostream>
using namespace std;
int main() {
int x = 19; // x is known to all code.
if(x == 19) {
int y = 20;
cout << "x + y is " << x + y << "\n";
}
// y not known here.
return 0;
}x + y is 39
