help with for loop with arrays

can someone tell me what am i doing wrong with for loop. its not returning what its suppose to. everything else works except for that.

Code:

#include <stdio.h>

int min();
int max();

main()
{
      double x[10], y[10], z[19];
      int c;
      int f;

        FILE *inp;
        int input_status;
        int i,t;
        double a,b;

        inp = fopen("input-xy.txt", "r"); //opens files
        input_status = fscanf(inp, "%d %lf %lf", &i,&a,&b); //takes digits

        while(input_status != EOF)
        {

                x[i]=a;
                y[i]=b;

                input_status = fscanf(inp, "%d %lf %lf", &i,&a,&b);
        }
                fclose(inp);
        for(t=1;t<=6;t++)
        printf("%lf %lf\n",x[t],y[t]);


      int j,q;
      double sum;

      for(j=0; j<=18; ++j)
      {
            c = max(j);        //cant figure out whats wrong with it
            f= min(j);
            sum=1;
            
            for(c;c<=f;c++)
                {  q=x[c]*y[j-c];
                   sum= sum + q;
                }
              z[j]=sum;
              printf("z[%d]= %lf\n",j,z[j]);
      }
system("pause");

}
int min(int j)
{       int min;
        if(9>=j)
           min=j;
        else if(9<=j)
        min=9;
        return min;
}

int max(int j)
{       int max;
        if((9-j)<=j)
           max=j;
        else if((9-j)>=j)
        max=(9-j);
        return max;
        }

Why do you think there's something wrong with it?

input_status = fscanf(inp, "%d %lf %lf", &i,&a,&b);

Is that what fscanf() returns?

yeah. the scanf works right i checked it. tje while loop assigns the elements arrays. but the for loop that is suppose to give me the summation doesnt work. since i say sum=1 it gives me 1 when i print


printf("z[%d]= %lf\n",j,z[j]);


. so it has to be that loop that isnt working properly. i am not sure whats wrong with it.

So when j equals zero, your max returns 9 and your min returns 0. Are you sure your for loop isn't supposed to go from min to max, rather than the other way around?