C# P175页7-7、7-9

7-7

源码：

using System;
namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] intArray = new int[20] {2,343,2,3,65,89,98,234,2,3,4,1,8,7,0,2,87,3,2,3};
            int index = 0;
            foreach (var item in intArray)
            {
                index++;
                if(item == 98)
                {
                    Console.WriteLine("值为{0}的元素在数组中的下标是：" + index,item);
                }
            }
        }
    }
}

7-9

源码：

using System;
namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            int sum = 0,i,j;
            int[,] intArr = new int[,]{{1,2,3,4,5},{6,7,8,9,10},{11,12,13,14,15},{16,17,18,19,20},{21,22,23,24,25}};
            for (i = 0; i < 5; i++)
            {
                for (j = 0; j < 5; j++)
                {
                    if ((i + j) % 2 == 0)
                        sum += intArr[i,j];
                }
            }
            Console.WriteLine("5×5矩阵两对角线元素之和为：" + sum);
        }
    }
}