Memory model

#include <iostream>
using namespace std;

int main(){
    int a;
    return 0;
}

In this code, we initialized a - however didn’t assign anything to a. When we declare a variable, we assign a memory space however we never assign a value - its point to a random memory.

#include <iostream>
using namespace std;

int main(){
    int a = 0;
    cout << a << endl;
    cout << &a << endl;
    
    a = 2;
    cout<< &a << endl;
    return 0;
}

(Example) Output:

0
0x16f976a68
0x16f976a68

Note that we uses & in here to see it’s memory address. And once we define the value it’s always pointing to the same position inside the pointer

Another example:

#include <iostream>
using namespace std;

int main(){
    int a = 0;
    int b = 0;
    int c = 0;
    int d = 0;
    cout << "Address of a: " << &a << endl;
    cout << "Address of b: " << &b << endl;
    cout << "Address of c: " << &c << endl;
    cout << "Address of d: " << &d << endl;
    return 0;
}

Address of a: 0x16afa2a68
Address of b: 0x16afa2a64
Address of c: 0x16afa2a60
Address of d: 0x16afa2a5c

Note that in here all of the memory are 4 bytes away, which implies that int ’s length is 4 bytes long.

And note in this program

#include <iostream>
using namespace std;

void modify(int &ref) {
    ref = 30;
    cout << &ref << endl;
}

int main(){
    int a = 10;
    cout << &a << endl;
    modify(a);
    cout << a << endl;
    return 0;
}

The output

0x16b226a68
0x16b226a68
30

Which we can see that inside the modify, the memory are the same

Alias &

#include <iostream>
using namespace std;

int main(){
    int a = 10;
    int b = 20;

    int &ref = a;
    return 0;
}

Value of ref: 10
Address of a: 0x16f412a68
Address of ref: 0x16f412a68

Both of the ref and a using the same address.

C++ Grammer

char: single character

To declare a variable of type char : char letter;

Character constants are enclosed in single quotes: char letter = 'x';

string: collection of chars

string is a class, different from the primitive data types.