Invalid Types Float[Int] for Array Subscript

I had been doing a question. I have not written the function code here because I am getting an error:

invalid types float[int] for array subscript in the following code snippet.

Please tell me why is this error coming?

#include<iostream>
using namespace std;
main()
{
    float a,b,p,q,r,s,arr[1000];
    int n=1000, minOp;

  cin>>a;
  cin>>b;
  cin>>p>>q>>r>>s;
  arr[0]=src;
  for(int i=1; i<n; i++)
  {
      if( i%4==1)
      {
          a[i]=a[i/4] + p;
      }
      else if( i%4==2)
      {
          a[i]=a[i/4] - q;
      }
      else
      if( i%4==3)
      {
          a[i]=a[i/4] * r;
      }
      else if( i%4==0)
      {

          a[i]= a[ (i/4)-1] / s;
      }
    }

 root = buildTree( arr, n);
 minOp = bfs(root,b);
cout<<minOp;
}

Any help would be appreciated.