what is call by reference in c++ language code example

Example 1: calling by reference c++

int main() {
    int b = 1;
    fun(&b);
    // now b = 10;
    return 0;
}

Example 2: calling by reference c++

void fun2(int& a) 
{
    a = 5;
}

int main()
{
    int b = 10;
    fun2(b); 

    // now b = 5;
    return 0;
}