Help me in solving CHFHEIST problem

My issue

Can someone expalin where did my code logic fail
include <bits/stdc++.h>
using namespace std;

int main() {

int T;
cin>>T;
while(T–)
{
int D;
cin>>D;
int d;
cin>>d;
int P;
cin>>P;
int Q;
cin>>Q;
int sum=0;
int x=1;
int y=P;
for(int i=1;i<=D;i++)
{
if(i==(xd+1))// As after every ‘d’ days the money get updated to P+qd this statment will find the next day from where the money will updated and make the change in rate.
{
y= P+ x
Q;
x++;
//sub=x*d;

    }
    
        sum=sum+y;
    
}
cout<<sum<<endl;

}
}

My code

#include <bits/stdc++.h>
using namespace std;

int main() {
	
int T;
cin>>T;
while(T--)
{
    int D;
    cin>>D;
    int d;
    cin>>d;
    int P;
    cin>>P;
    int Q;
    cin>>Q;
    int sum=0;
    int x=1;
    int y=P;
    for(int i=1;i<=D;i++)
    {  
        if(i==(x*d+1))
        {   
            y= P+ x*Q;
            x++;
            //sub=x*d;
            
        }
        
            sum=sum+y;
        
    }
    cout<<sum<<endl;
}
}

Problem Link: Bella ciao Practice Coding Problem