Getting the error: invalid type argument of unary ‘*’ (have ‘double’)

I tried to troubleshoot this and couldn’t find the exact problem as to why I’m getting this error(error: invalid type argument of unary ‘*’ (have ‘double’)
*outerD_P = outerD;) . I tried making innerD_P and outerD_P a ** but that didn’t work. I’m sorry if it’s a simple fix I’m still learning C. Thank you for the help

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

// PI is the ratio of diameter to the circumfrence of a circle
#define PI 3.1415


int main(int argc, const char *argv[])
{

  double weight, volume, batchWeight, innerA, outerA, area;
  double innerD, outerD, density, thickness;
  double* volume_P, density_P, innerA_P, outerA_P, area_P, thickness_P;
  double* innerD_P, outerD_P;
  int quantity;
  int* quantity_P;


  //variables that point to the corresponding command line arguments beleow:
  innerD = atof(argv[1]);
  outerD = atof(argv[2]);
  thickness = atof(argv[3]);
  density = atof(argv[4]);
  quantity = atoi(argv[5]);

  //Not allowing the user to enter a 0 for quantity must have atleast ONE washer
  if(quantity < 1)
  {
    printf("Quantity can not be less than 1! Try again\n.");
    return 0;
  }

  //setting the pointer equal to the command line input
   *innerD_P = innerD;
   *outerD_P = outerD;

    innerA = PI*pow(*innerD_P/2, 2);
    outerA = PI*pow(*outerD_P/2, 2);

>Solution :

double* volume_P, density_P, innerA_P, outerA_P, area_P, thickness_P;
double* innerD_P, outerD_P;

In those lines the * only binds to the next variable. It means that the above is actually declaring only the first variable on each line as a pointer and all the rest are double.

Change to:

double *volume_P, *density_P, *innerA_P, *outerA_P, *area_P, *thickness_P;
double *innerD_P, *outerD_P;