2. Variables and scope

1. Variable

Use and define , And can be initialized with an expression .

#include <iostream>
using namespace std;

int main()
{
    double a = 12 * 3.25;
    double b = a + 1.112;
    cout << a << endl;
    cout << b << endl;
    a = a * 2 + b;
    double c = a + b * a;
    cout << c << endl;
    return 0;
}

Block {} Internal scope can define variables with the same name outside the domain , The external variables are hidden in this fast .

#include <iostream>
using namespace std;

int main()
{
    double a;
    cin >> a;
    {
        int a = 1;
        a = a * 10 + 4;
        cout << a << endl;
    }
    cout << a << endl;
    return 0;
}

for Loops can define local variables .

#include <iostream>
using namespace std;

int main()
{
    int i = 0;
    for (int i = 0; i < 4; i++)
    {
        cout << i << endl; //  Output loop local variable 
    }

    cout << i << endl; //  Output main Medium i
    
    for (i = 0; i < 4; i++)
    {
        for (int i = 0; i < 4; i++) // Redefine local variables for each round i
        {
            cout << i << " ";
        }
        cout << endl;
    }
    return 0;
} 

Access the global variable with the same name as the variable of the internal scope , To qualify with global scope ::.

#include <iostream>
using namespace std;

double a = 123;

int main()
{
    double a = 256;

    cout << a << endl; // local variable a
    cout << ::a << endl; // Global variables a

    return 0;
}