C++ Tutorial/Language Basics/Variables
Содержание
A scoping example
<source lang="cpp">#include <iostream> using std::cout; using std::endl; void useLocal( void ); void useStaticLocal( void ); void useGlobal( void ); int x = 1; int main() {
int x = 5;
cout << x << endl;
{
int x = 7;
cout << "local x in main"s inner scope is " << x << endl;
}
cout << x << endl;
useLocal();
useStaticLocal();
useGlobal();
useLocal();
useStaticLocal();
useGlobal();
cout << x << endl;
return 0;
} void useLocal( void ) {
int x = 25; cout << "local x is " << x << " on entering useLocal" << endl; x = x + 20; cout << "local x is " << x << " on exiting useLocal" << endl;
} void useStaticLocal( void ) {
static int x = 50;
cout << "local static x is " << x << " on entering useStaticLocal"
<< endl;
x = x + 20;
cout << "local static x is " << x << " on exiting useStaticLocal"
<< endl;
} void useGlobal( void ) {
cout << "global x is " << x << " on entering useGlobal" << endl; x = x + 20; cout << "global x is " << x << " on exiting useGlobal" << endl;
}</source>
5 local x in main"s inner scope is 7 5 local x is 25 on entering useLocal local x is 45 on exiting useLocal local static x is 50 on entering useStaticLocal local static x is 70 on exiting useStaticLocal global x is 1 on entering useGlobal global x is 21 on exiting useGlobal local x is 25 on entering useLocal local x is 45 on exiting useLocal local static x is 70 on entering useStaticLocal local static x is 90 on exiting useStaticLocal global x is 21 on entering useGlobal global x is 41 on exiting useGlobal 5
Assign value to a variable
<source lang="cpp">#include <iostream> using namespace std;
int main() {
int length; // this declares a variable length = 7; // this assigns 7 to length cout << "The length is "; cout << length; // This displays 7 return 0;
}</source>
The length is 7"
Comparing data values
<source lang="cpp">#include <iostream> using std::cin; using std::cout; using std::endl; int main() {
char first = 10;
char second = 20;
cout << "The value of the expression first < second is: "
<< (first < second)
<< endl
<< "The value of the expression first == second is: "
<< (first == second)
<< endl;
return 0;
}</source>
The value of the expression first < second is: 1 The value of the expression first == second is: 0
Dynamic initialization.
<source lang="cpp">#include <iostream> using namespace std;
int main() {
double radius = 4.0, height = 5.0; // dynamically initializ volume double volume = 3.1416 * radius * radius * height; cout << "Volume is " << volume; return 0;
}</source>
Volume is 251.328"
Finding maximum and minimum values for data types
<source lang="cpp">#include <limits>
- include <iostream>
using std::cout; using std::endl; using std::numeric_limits; int main() {
cout << "The range for type short is from "
<< numeric_limits<short>::min()
<< " to "
<< numeric_limits<short>::max();
cout << "The range for type int is from "
<< numeric_limits<int>::min()
<< " to "
<< numeric_limits<int>::max();
cout << "The range for type long is from "
<< numeric_limits<long>::min()
<< " to "
<< numeric_limits<long>::max();
cout << "The range for type float is from "
<< numeric_limits<float>::min()
<< " to "
<< numeric_limits<float>::max();
cout << "The range for type double is from "
<< numeric_limits<double>::min()
<< " to "
<< numeric_limits<double>::max();
cout << "The range for type long double is from "
<< numeric_limits<long double>::min()
<< " to "
<< numeric_limits<long double>::max();
cout << endl;
return 0;
}</source>
The range for type short is from -32768 to 32767The range for type int is from - 2147483648 to 2147483647The range for type long is from -2147483648 to 214748364 7The range for type float is from 1.17549e-038 to 3.40282e+038The range for type double is from 2.22507e-308 to 1.79769e+308The range for type long double is fr om 0 to 1.#INF
Using the unary scope resolution operator
<source lang="cpp">#include <iostream> using std::cout; using std::endl; int n = 7; int main() {
double n = 10.5;
cout << "Local double value of n = " << n
<< "\nGlobal int value of n = " << ::n << endl;
return 0;
}</source>
Local double value of n = 10.5 Global int value of n = 7
