问如何在C编程中获得预期的输出？

EN

   #include<stdio.h>
    
    int main() 
{
      printf("\t\tWELCOME TO UNIMAP LAUNDRY");
      
     printf("\nThis program is to display laundry price paid by customers\n");

      float l, W, sum, r;

      for (l = 0; l < 4; l++) {
        printf("Please enter laundry weight(kg):");
        scanf("%f", & W);

        printf("Total amount to pay is RM%f\n", r);

        if (W < 1)
          r == (W * 1.2);
        else if (W < 7)
          r == (W * 0.9);
        else if (W < 12)
          r == (W * 0.6);
        else
          r == (W * 0.7);
      }

      sum += r;

      printf("The total sales are RM%f", sum);
      return 0;
    }

WELCOME TO UNIMAP LAUNDRY
This program is to display laundry prices paid by customers
Please enter laundry weight(kg):12
The total amount to pay is RM0.000000
Please enter laundry weight(kg):6
The total amount to pay is RM0.000000
Please enter laundry weight(kg):5
The total amount to pay is RM0.000000
Please enter laundry weight(kg):9
The total amount to pay is RM0.000000
The total sales are RM-29726079709203136512.000000