程序代码：

//计算油耗--数组使用示例

#include <iostream>
#include <iomanip>
using namespace std;

int main ( )
{
   
    const int MAX = 20;
    double gas[ MAX ];
    long miles [ MAX ];
    int count = 0;
    char indicator = 'y';                                               //默认值设为 'y'，在下面的 while 循环中要用到

    while((indicator == 'y' || indicator == 'Y') && count < MAX)
    {
        cout << endl
            << "Enter gas quantity: ";
        cin >> gas[count];                                               //输入购买的汽油
        cout << "Enter odometer reading: ";
        cin >> miles[count];                                             //跑了多少路程
       
        ++count;                                                         //计数器自加 1
        cout << "Do you want to enter another( y or n)? ";
        cin >> indicator;                                                //循环计算
    }

    if( count <= 1)                                                      //如果只输入一对数据，则无结果退出
    {
        cout << endl
            << "Sorry - at least two readings are necessary. ";

        //system("pause");
        return 0;
    }

    for( int i = 1; i < count; i++)                                      //计算次数 i 小于 count ，比如 count 为 4, i 为 3
    {
        cout << endl
        << setw(2) << i << "."
        << "Gas purchased = " << gas[i] << "Gallons "
        << "resulted in "
        << ( miles[i] - miles[i-1]/gas[i]) << " miles per gallon.";
        cout << endl;
    }
       
       
        system("pause");
        return 0;
}