Thread: Structure difficulties

I get the error message: dereferencing pointer to incomplete type
for every line where i use the code line: pointer->variableinstructure

Code:

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

struct OUTPUT_DATA 
{
       int C_num; 
       int P_num; 
       int B_num; 
       float Prix_C; 
       float Prix_B; 
       float Prix_P;
};

void Output_Data(struct OUTPUT_DATA *);

int main()
{
      //All my variables are declared, i double checked....

      struct OUTPUT_DATA NUM_COST;
     
      NUM_COST.C_num = ((sortieHeureMaxPanneaux / eff_conv) / 5) + 1;
      NUM_COST.B_num = ((Besoin / eff_conv) / 4.8) + 1;
      NUM_COST.P_num = Aire + 1;
      
      NUM_COST.Prix_C = NUM_COST.C_num * C$;
      NUM_COST.Prix_B = NUM_COST.B_num * B$;
      NUM_COST.Prix_P = NUM_COST.P_num * P$;

      Output_Data(NUM_COST);

      system("PAUSE");
      return 0;
}

void Output_Data(struct OUTPUT_DATA *NUM_COSTptr)
{
      char article[3][29] = {"Batteries (4.8 V)","Convertisseurs (5 KW)","Panneaux photovoltaique (m^2)"};
      float $Total;
      
      printf("\nAfin d’installer un bloc d’alimentation &#233;lectrique photovolta&#239;que &#224; panneaux plats pour l’utilisation r&#233;sidentielle &#224; Ottawa, ON, vous aurez besoin de:\n\n");
      printf("&#37;d %s = %f", NUM_COSTptr->B_num, article[0], NUM_COSTptr->Prix_B);
      printf("\n%d %s = %f", NUM_COSTptr->C_num, article[1], NUM_COSTptr->Prix_C);
      printf("\n%d %s = %f", NUM_COSTptr->P_num, article[2], NUM_COSTptr->Prix_P);
      
      $Total = NUM_COSTptr->Prix_B + NUM_COSTptr->Prix_C + NUM_COSTptr->Prix_P;
      
      printf("\n\nCouts total: %f", $Total);
}