5.1 Arrays

So far in constructing our building we have named each brick (variable). That is fine for a small number of bricks, but what happens when we want to construct something larger? We would like to point to a stack of bricks and say, "That's for the left wall. That's brick 1, brick 2, brick 3. . . ."

Arrays allow us to do something similar with variables. An array is a set of consecutive memory locations used to store data. Each item in the array is called an element. The number of elements in an array is called the dimension of the array. A typical array declaration is:

// List of data to be sorted and averaged
int    data_list[3]; 

This declares data_list to be an array of the three elements data_list[0], data_list[1], and data_list[2], which are separate variables. To reference an element of an array, you use a number called the subscript (the number inside the square brackets [ ]). C++ is a funny language and likes to start counting at 0, so these three elements are numbered 0-2.

Common sense tells you that when you declare data_list to be three elements long, data_list[3] would be valid. Common sense is wrong: data_list[3] is illegal.

Example 5-1 computes the total and average of five numbers.

Example 5-1. five/five.cpp

#include <iostream>

float data[5];  // data to average and total 
float total;    // the total of the data items 
float average;  // average of the items

int main(  )
{
    data[0] = 34.0;
    data[1] = 27.0;
    data[2] = 46.5;
    data[3] = 82.0;
    data[4] = 22.0;

    total = data[0] + data[1] + data[2] + data[3] + data[4];
    average =  total / 5.0;
    std::cout << "Total " << total << " Average " << average << '\n';
    return (0);
}

Example 5-1 outputs:

Total 211.5 Average 42.3