Exercise 1.6

Write a program to read in a sequence of integers from standard input. Place the values, in turn, in a built-in array and a vector. Iterate over the containers to sum the values. Display the sum and average of the entered values to standard output.

The built-in array and the vector class differ in primarily the same ways as the C-style character string (which is implemented as an array of char elements) and the string class: (1) The built-in array must be of a fixed size, whereas the vector can grow dynamically as elements are inserted, and (2) the built-in array does not know its size. The fixed-size nature of the built-in array means that we must be concerned with potentially overflowing its boundary. Unlike the C-style string, the built-in array has no sentinel value (the null) to indicate its end. Particularly for beginners, I recommend that the vector class be used in favor of the built-in array. Here is the program using the vector class:

#include <iostream> 


#include <vector> 


using namespace std; 





int main() 


{ 


    vector<int> ivec; 


    int ival; 


    while ( cin >> ival ) 


            ivec.push_back( ival ); 





    // we could have calculated the sum as we entered the 


    // values, but the idea is to iterate over the vector ... 


    for ( int sum = 0, ix = 0; ix < ivec.size(); ++ix ) 


          sum += ivec[ ix ]; 





    int average = sum / ivec.size(); 


    cout << "Sum of " << ivec.size() 


         << " elements: " << sum 


         << ". Average: " << average << endl; 


} 

The primary difference in the following built-in array implementation is the need to monitor the number of elements being read to ensure that we don't overflow the array boundary:

#include <iostream> 


using namespace std; 





int main() 


{ 


    const int array_size = 128; 


    int ia[ array_size ]; 


    int ival, icnt = 0; 





    while ( cin >> ival && 


            icnt < array_size ) 


                 ia[ icnt++ ] = ival; 





    for ( int sum = 0, ix = 0; ix < icnt; ++ix ) 


          sum += ia[ ix ]; 





    int average = sum / icnt; 


    cout << "Sum of " << icnt 


         << " elements: " << sum 


         << ". Average: " << average << endl; 


}