Is there any in-built function or header file I need to add for Single Inheritance?

This Single Inheritance code has no error but when I run this void the function void B::get_ab() gets executed first as expected but the line which is second in the function(cin>>a>>b;) gets executed first and the first line, anyone know whats happening here? Thank you!

#include<iostream>
#include<stdio.h>

using std::equal_range;
using std::lower_bound;
using std::upper_bound;
using std::pair;
using std::string;
using std::getline;
using std::vector;
using std::cout;
using std::ios;
using std::set;
using std::cin;

class B
{
    int a;
    public: int b;
    void get_ab();
    int get_a(void);
    void show_a(void);
};
class D:private B{
    int c;
    public: void mult();
    void display();
};
void B::get_ab()
{
   
    cout<<"Enter values of a&b";
    cin>>a>>b;
}
int B::get_a()
{
    return a;
}
void B::show_a()
{
    cout<<"a="<<a<<"\n";
}
void D::mult()
{
    get_ab();
    c=b*get_a();
}
void D::display()
{
    show_a();
    cout<<"b="<<b<<"\n"<<"c="<<c<<"\n";
}
int main()
{
   ios::sync_with_stdio(0);
   cin.tie(0);
   D d;
   d.mult();
   d.display();
   return 0;
}```