3.13

代码说明：

  读一组整数到vector对象，计算并输出每对相邻元素的和。如果读入元素个数为奇数，则提示用户最后一个元素没有求和，并输出其值。(Read a set of integers to vector objects, calculate and output, and each pair of adjacent elements. If you read an odd number of elements, the last element of the user is prompted no summation, and output its value.)