Compound Interest Formula

#include <cstdio>
#include <math.h>  
#include <iostream>

using namespace std;

int main ()
{
double dollars, amount, interest, power, formularate; 
int days, rate;
bool notValid;
int a=1;
   
   do{
   notValid=false;                                       //Validation for amount
   cout << "\nPlease enter dollar starting amount?" ; 
   cin >> dollars;
   if (dollars <10 || dollars >10000)
       {
        cout << "\nYou have entered invalid data"; 
        notValid=true;
        }
   } while (notValid);

   do{
   notValid=false;                                       //Validation for rate
   cout << "\nWhat is the daily increase (as a percentage)?" ;
   cin >> rate;
   if (rate <1 || rate >22)
       {
        cout << "\nYou have entered invalid data"; 
        notValid=true;
        }
   } while (notValid);
  
   do{
   notValid=false;                                       //Validation for days
   cout << "\nEnter the number of days:" ;
   cin >> days;
   if (days<2 || days >30)
       {
        cout << "\nYou have entered invalid data"; 
        notValid=true;
        }
   } while (notValid);
  
   {
       cout << "\n\nDay     Earned Interest     Balance"; 
       cout << "\n-----------------------------------\n";
        
       
        for(a==1; a <= days; )                           //Loop for display 
                { 
                  formularate=(rate/100);
                  amount=dollars*pow(1+(formularate/365),(a));
                  interest=amount-dollars;                     
                  cout << a;
                  cout << "           ";  
                  cout << interest; 
                  cout << "               "; 
                  cout << amount;  
                  cout << "               "; 
                  cout <<"\n\n";                  
                  a++;                                                     }      
            system("pause");
            

    }
}