1. Code help; loop problem

Hi,

I have the following program. It worked great until I added the For loop at the begining, and modified if((i=0)&&(doy <=1)). Now the output looks good for a couple iterations, but then goes into this endless output of day nan nan nan ~0.035 nan nan nan nan. Any suggestions on how to fix this problem? Many thanks!

The code:

Code:
```#define SMA 0.00036			/* DIM scaling parameter for SM curve */
#define SMB 105.0			/* DIM scaling parameter for SM curve */
#define FMET 0.59			/* DIM metabolic fraction of NPP; Potter et al. 1993, CHANGE FOR DIFFERENT BIOMES */
#define FSTR 0.70			/* DIM slow SOC fraction of structural SOC pool; Ise and Moorcroft 2006 */
#define KSTR 0.40			/* DIM proportional rate K for structural SOC decomposition; Ise and Moorcroft 2006 */
#define KSLW 0.0093			/* DIM proportional rate K for slow SOC decomposition; Ise and Moorcroft 2006 */
#define FRAUT 0.53			/* DIM proportion of GPP represented by autotrophic respiration. This value is taken from Choudhury (2001). The origional model used Gifford et al. 2005,
**                          /* value of 0.46.  CHANGE FOR DIFFERENT BIOMES */

#define ME 0.45				/* DIM Microbial efficiency; McGill et al. 1981; Potter et al. 1993 */
#define KOPT 0.0301			/* Optimal decomposition rate (1/d) for soil metabolic fraction; Ise and Moorcroft 2006 */

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

int main()

{

int	doy;
doy=0;

double	soil_t;		/* surface soil temperature; deg K */
double	soil_m;		/* surface soil moisture; % saturation */
double	gpp;		/* GPP; g C m-2 d-1 */

double  npp;

double rmet;
double rstr;
double rslw;

double	npp_ann_init;	/* Initial NPP pool; g C m-2 yr-1 */
double	soil_t_av;	/* long-term avg surface soil T; deg K */
double  soil_m_av; 	/* long-term avg JJA soil moisture; % saturation */
double  met_c_init;	/* initial soil metabolic C pool; g C m-2; Ise and Moorcroft, 2006 */
double  struct_c_init;	/* initial structural soil C pool; g C m-2; Ise and Moorcroft, 2006 */
double  slow_c_init;	/* initial slow soil C pool; g C m-2; Ise and Moorcroft, 2006 */
double  r_aut;		/* autotrophic respiration; g C m-2 d-1 */
double  r_het;		/* heterotrophic respiration; g C m-2 d-1 */

double dCmet;
double dCstr;
double dCslw;

double cmet;
double cstr;
double cslw;

double  r_tot;		/* total respiration; g C m-2 d-1 */
double  k_met_opt;	/* optimal soil metabolic C decomposition rate; d-1 */
double  k_met_av;	/* average soil metabolic C decomposition rate; d-1 */
double  k_met;		/* actual soil metabolic C decomp rate; d-1 */
double  k_struct;	/* soil structural C decomp rate; d-1 */
double  k_slow;		/* soil slow C decomp rate; d-1 */

double  tmult;		/* DIM 0-1, soil temperature rate response curve */
double  tmult_av;	/* DIM 0-1, soil temperature rate response under avg conditions */
double  wmult;		/* DIM 0-1, soil moisture rate response curve */
double  wmult_av;	/* DIM 0-1, soil moisture rate response under avg conditions */
int     flag;		/* DIM 0.0 or 1.0 for spinup or daily run, respectively */

/* 1.0 open data input file */

FILE *datain;

int i;
i=1;

for (i = 0 ; i < 2; i++)

{

/* datain =fopen("/home/jennifer.watts/Carbon_Models/TCF_model_modified/Testing_Spinup/", "r"); */
datain =fopen("tcf_spinup.txt", "r");

if (datain == NULL)
{
fprintf(stderr, "Can't open input file!\n");
exit(-1);
}

while(fscanf(datain,"%d %d %lf %lf %lf %lf %lf %lf %lf %lf %lf",
&flag, &doy, &gpp, &soil_t, &soil_m, &soil_t_av, &soil_m_av, &npp_ann_init, &met_c_init, &struct_c_init, &slow_c_init) != EOF)
{

doy++;

/* address inital values for year 1, day 1, of spin-up*/

if((i=0) && (doy <= 1 ))
{
cmet = met_c_init;
cstr = struct_c_init;
cslw = slow_c_init;
rmet = 0;
rstr = 0;
rslw = 0;
}

/* 3.0 Environmental Constraint Calculations*/

k_met_opt = KOPT;

/* calculate soil temperature rate response (Lloyd and Taylor 1994) */

tmult = exp(308.56 * ((1.0 / 66.02) - (1.0 / ((soil_t) - 227.13))));

/* calculate soil moisture response (Monsi 1969, Bunnell and Tait 1974, Oberbauer et al. 1991, 1996) */

wmult = SMA * (SMB * soil_m - pow(soil_m, 2.0));

/* 4.0 Calculate soil CO2 input and output; soil C pool values */

/* calculate decomposition rate constants */

k_met = k_met_opt * tmult * wmult;
k_struct = KSTR * k_met;
k_slow = KSLW * k_met;

rmet = (k_met * cmet * (1.0 - ME));
rstr = (k_struct * cstr * (1.0 - ME));
rslw = (k_slow * cslw * (1.0 - ME));

r_het = (rmet + rstr + rslw);

r_aut = (gpp * FRAUT);

r_tot = (r_het + r_aut);

npp = (gpp - r_aut);

dCmet = (FMET * npp - rmet);
dCstr = (((1 - FMET) * npp) - rstr - FSTR * cstr);
dCslw = ((FSTR * cstr) - rslw);

cmet += (cmet + dCmet);
cstr += (cstr + dCstr);
cslw += (cslw + dCslw);

/* print out daily updating of carbon pools for spinup run */

printf("%d %.3f %.3f %.3f %.3f %.3f %.3f %.3f %.3f\n", doy, cmet, cstr, cslw, npp, r_tot, dCmet, dCstr, dCslw);
}

fclose(datain);

}

}```

2. Code:
`	  if((i=0) && (doy <= 1 ))`
= is for assignment.
== is for comparison.

You have in effect: if( 0 && doy <= 1 ) which immediately fails, because 0 && anything is false.

Quzah.

3. quzah pointed out one of the biggest mistakes beginners make. Be careful not to get the assignment operator and the relational operator mixed up.

4. Thanks so much!

It seems to be working just fine now.