// Example of why file-scoped entities are usually undesirable 
// substitutes for parameters.
//
// Note how a user of printList() is limited by the function's
// dependence on an external value.
//
#include <stdio.h>

#define SZ 10
void initWithSquares(int List[]);
void initWithDiffs(int Target[], int Source[]);
void printList(FILE* fp, int List[]);

int main() {

   FILE *Out = fopen("listing.txt", "w");
   
   int A[SZ] = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29};
   
   initWithSquares(A);     // This is all OK.
   fprintf(Out, "A:\n");
   printList(Out, A);
   
   int B[SZ-1];
   initWithDiffs(B, A);
   fprintf(Out, "B:\n");
   printList(Out, B);      // But printList() has no way to discover
                           // how many values are in B...
   
   fclose(Out);
   return 0;
}

void initWithSquares(int List[]) {

   for (int i = 0; i < SZ; i++) {
      List[i] = i*i;
   }    
}

void initWithDiffs(int Target[], int Source[]) {

   for (int i = 0; i < SZ-1; i++) {
      Target[i] = Source[i+1] - Source[i];
   }
}

void printList(FILE* fp, int List[]) {

   for (int i = 0; i < SZ; i++) {
      fprintf(fp, "%5d:  %d\n", i, List[i]);
   }
}