280: Mainline

Now suppose that you want to fill an array using data in a file. You probably do not know exactly how many objects you need to store. Accordingly, you need an approach to dealing with uncertainty.

One approach, about which you learn in the hardcopy version of this book, is to limit wasted memory by allocating memory for objects at run time. In this chapter, you learn about a simpler approach: You define an object array that is sure to be large enough to hold all the objects you can possibly encounter. Then, you proceed to fill that array using a while reading or for reading pattern.

In the following program, for example, you create two arrays, each of which can hold up to 100 integers representing the prices per share and the numbers of shares involved in a group of trades. Then, you fill part or all of that array with floating-point numbers and integers using a for reading pattern in which the value of the limit variable is counted up to the total number of price–number pairs. Finally, you use another for loop to add up the products of the numbers:

#include   
/* Define trade_price */ 
double trade_price (double p, int n) { 
  return p * n; 
} 
/* Define global arrays */ 
double price[100]; 
int number[100]; 
main ( ) { 
  /* Declare various variables */ 
  int limit, counter; 
  double sum = 0.0; 
  /* Read numbers and stuff them into arrays */ 
  for (limit = 0;  
       2 == scanf ("%lf%i", &price[limit], &number[limit]); 
       ++limit) 
    ; 
  /* Add all products of corresponding elements in the two arrays */ 
  for (counter = 0; counter < limit; ++counter) 
    sum = sum + trade_price (price[counter], number[counter]); 
  /* Display sum */ 
  printf ("The total value of the %i trades is %f.\n", 
                                  limit,       sum); 
} 
--- Data ---
10.2    600     12.0    100     13.2    200 
--- Result --- 
The total value of the 3 trades is 9960.000000.