I would REALLY appreciate any help anyone could give on this program
as to why it is not doing what it should. This program is supposed to
use the multi-aray 'index' as a lookup table for calculating the wind
chill factor. Temperature is on the x axis and Wind velocity is on the
y axis. It would be a simple lookup with array subscripting except my
instructor threw a twist on it. He wants it to calculate any number
entered. (Each row and columns are in multiples of 10) So if a user
enters a temp of 12 and wind velocity of 23 then the computer can
figure it by linear interpolation. My instructor said to use the
distance formula for getting the distance to each of the corners
(do,d1,d2,d3) then to take those numbers and plug them into a weight
function. The formulas are in the program but something isn't working
right. Another immediate problem is that I JUST began using a macro
definition (SQR) and for some reason it isn't working. It keeps giving
me a 'undefined x' error. I am not sure how to #define this macro so
that it will work with my formulas. Well you could have a field day
with this program. If you can make any sense out of it at all, you
have my respect! Please ask any questions for more info if you need
it. I even asked the c.s. tutor and he couldn't even figure this one
out.

Thanks again,
Ryan

The terror begins here:
-------------------------------------------------------------------------------------------

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

#define SQR ((x)*(x))
#define NUM_TEMP 9
#define NUM_WIND 6

void error(void);

main()
{
  int itemp=0, iwind=0, d0=0, d1=0, d2=0, d3=0, wc=0, nd0=0, nd1=0,
nd2=0, nd3=0;
  double temp=0, wind=0, ftemp=0, fwind=0, ntemp=0, nwind=0;
  double index[NUM_TEMP][NUM_WIND] = /*I moved the array down for
clarity */
{{-20, -30, -55, -80, -105,-115},
 {-10, -20, -46, -63, -82,  -102},
 {  0,  -14,   -33, -52, -68,  -78 },
 { 10,  -5, -18, -35, -57,  -75    },
 { 20, 1, -12, -28, -42, -62       },
 { 30,  10,  -2, -14, -24,  -34    }
{ 40,  21,   8,  -1, -10,    -29    },
{ 50,  33,  22,  11,   2,  -8        },
{ 60,  42,  38,  22,  -9,   12     }};

  puts("Enter temperature (in F, 50 to -20): ");
  scanf("%lf", &temp);
        if (temp > 59 || temp < -20)
                error();                                                                                                                /* Give an error */

  puts("Enter wind speed (in MPH): ");
  scanf("%lf", &wind);
    if (wind > 49 || wind < 0)
                error();                                                                                                        /* Give an error */

  ntemp = ((temp + 20) / 10);
  nwind = (wind / 10);

  ftemp = temp - (int) temp;
  fwind = wind - (int) wind;

  itemp = ntemp - (float) temp;
  iwind - nwind - (float) wind;

  d0=sqrt((SQR(ntemp-ftemp)) + (SQR(nwind-fwind)));
  d1=sqrt((SQR(ntemp-ftemp)) + (SQR(nwind-fwind)));
  d2=sqrt((SQR(ntemp-ftemp)) + (SQR(nwind-fwind)));
  d3=sqrt((SQR(ntemp-ftemp)) + (SQR(nwind-fwind)));

  nd0=(SQR(1.4142135623 - d0) / 2);
  nd1=(SQR(1.4142135623 - d1) / 2);
  nd2=(SQR(1.4142135623 - d2) / 2);
  nd3=(SQR(1.4142135623 - d3) / 2);

wc=(nd0*index[itemp][iwind])+(nd1*index[itemp+1][iwind])+(nd2*index[itemp][iwind+1])+(nd3*index[itemp+1][iwind+1]);

  printf("\n\nThe wind chill factor would be: %g Degrees
Fahrenheit.",wc);

  return 0;

   exit (1);

The SQR macro should read...

        #define SQR(x) ((x) * (x))

Even with that fix, the program gives weird results!

Stephan

        #define SQR(x)    ( (x) * (x) )

    Perhaps you should output intermediate results between your
    calculations, to check that you're getting the right numbers at
    each step.