Im stuck.

I'm still a rookie with C and I'm calculating some thermodynamic parameters for meteorology and want to show the freezing levels. I can get it too show all heights that are 0 degrees C or lower... but I want it to only show the 1 or 2 levels that the temp changes from positive to zero or lower. Data file example would be

height	temp
100	10
1000	-2
1500	5
2000	-7
2500	-15

I would want it to say there is a freezing level at 1000 and 2000 meters. Any help would be great!

Posting your code so far would help as well.

Code:

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

int main()
{

 float P, h, T, DpT;  // P=pressure, h=height, T=temperature, DpT=dewpoint temp
 int i;                // counter for loop
 int j;                // counter for loop
 float K, km;          // K=Temp in Kelvin, km=height in kilometers, LR=Lapse Rate
 float esw;                // saturation vapor pressure over water
 float esi;                  // saturation vapor pressure over ice
 float height[500];          // array of heights in kilometers
 float tempC[500];          // array of temp in celcius
 float tempK[500];            // array of temp in kelvin
 float pressure[500];        // array of pressures
 float dewpt[500];          // array of dewpoint temps
 float BP = 373;            // Boil point at 1 atm
 float TP = 273.16;            // Triple point
 float estw = 1013.25;        // saturation vapor pressure at the steam-point pressure
 float esi0 = 6.1173;            // saturation vapor pressure at the ice-point pressure
 float part1, part2, part3, part4, part5, part6;    // parts of Goff-Gratch formula

 const int header_length = 0;
 char buff[256];
 j = 0;

FILE *input;

  input = fopen("KLM_ama.txt","r"); //input data file

  if(input == NULL)              //input check
    {
      printf("check your file name!\n");
      return(0);
    }

  for(i=0; i<header_length; i++)
    {
        fgets(buff,265,input);
    }

  while(fgets(buff,256,input))
    {
      fscanf(input,"%f %f %f %f", &P,&h,&T,&DpT);

        tempC[j] = T;
        pressure[j] = P;
        dewpt[j] = DpT;

        K = tempC[j] + 273;                  // Convert to Kelvin
        km = h/1000;                          // Convert height to kilometer

        tempK[j] = K;
        height[j] = km;

  //  printf("%5.0f %5.2f %f \n",pressure[j],height[j],tempK[j]);
        j++;
    }

  for(j=0; j<200; j++)
    {
      if(tempK[j]>223 && tempK[j]<375)      // calculation over water
        {
        part1 = -7.90298*((BP/tempK[j])-1)+5.02808*log10(BP/tempK[j]);

        part2 = 0.00000013816*((pow(10,11.344*(1-(tempK[j]/BP))))-1);

        part3 = 0.0081328*((pow(10,-3.49149*((BP/tempK[j])-1)))-1);

        esw = (pow(10,part1-part2+part3+log10(estw)));

      //  printf("Saturation vapor pressure over water is %5.2f hPa at %5.0f mb \n", esw, pressure[j]);
        }

      if(tempK[j]<273 && tempK[j]>173)    // calculation over ice
        {
        part4 = -9.09718*((TP/tempK[j])-1);

        part5 = 3.56654*log10(TP/tempK[j]);

        part6 = .876793*(1-(tempK[j]/TP));

        esi = (pow(10,part4-part5+part6+log10(esi0)));

      //  printf("Saturation vapor pressure over ice is %5.3f hPa at %5.0f mb \n", esi, pressure[j]);

        }
      }

  for(j=0; j<1; j++) // calculation of LCL
    {
      float LCL;
      LCL = ((tempC[j]-dewpt[j])/2.5)*304.8;

      printf("LCL hieght is %5.2f meters\n", LCL);
    }

  for(j=0; j<200; j++) // calculation of freezing levels
    {
      if(tempC[j]<0)
      {
      printf("freezing levels at: %5.2f hpa\n", pressure[j]);
      }
    }

}

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Code:

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// loop over heights
for ( h = 1 ; h < n ; h++ ) {
  if ( (temp[h-1] < 0 && temp[h] >= 0)  ||
      (temp[h-1] >= 0 && temp[h] < 0) ) {
    // transition
  }
}

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Thanks a bunch!