I'm writing a program that takes the length and width of a rectangular yard and house then computes the time required to cut the grass at two square feet a second. The final output my program gives is "NaN". Does anyone have any advice how I could write this better and produce better results? Thanks in advance. Here is what I have so far:

Code:/* Filename: mow.c Description: Compute the required time to cut grass at two square feet a second. */ #include <stdio.h> #include <math.h> int main() { /* memory allocation for data */ double ylength,ywidth,hlength,hwidth,yarea,harea,grasqyd,grasqft,time; /* prompt user for data */ printf ("Enter the length of the yard in feet (eg.20):"; scanf ("%lf",& ylength); printf ("Enter the width of the yard in feet (eg.20):"); scanf ("%lf",& ywidth); printf ("Enter the length of the house in feet (eg.20):"); scanf ("%d",& hlength); printf ("Enter the width of the house in feet (eg.20):"); scanf ("%lf",& hwidth); /* compute the total area of grass */ yarea = ylength * ywidth; harea = hlength * hwidth; grasqyd = yarea - harea; grasqft = grasqyd * 9; /* compute the time required */ time = grasqft/2; /* display result */ printf ("The time required to cut the grass at a rate of two square feet a\n" "second is %f \n",time); /* End */ return 0; }