，采用多线程的方法计算一个数组的各个元素之和。具体来说，该数组为 整型数组 a，有 300 个元素。在 main 函数中，对该数组的每个元素进行赋值，值为一 个 1-100 的随机数。然后创建 3 个线程，第 1 个线程负责计算 a[0]～a[99]这 100 个元素 之和；第 2 个线程负责计算 a[100]～a[199]这 100 个元素之和；第 3 个线程负责计算 a[200]～a[299]这 100 个元素之和。最后在 main 函数中汇集各个线程的计算结果，然后 算出最终的结果，即 a[0]～a[299]这 300 个元素的总和，并且打印出来。 -Multithreading method to calculate a sum of the individual elements of the array. Specifically, the array is an array of integers a, there are 300 elements. In the main function, the assignment of each element of the array, a value of a random number　1 to 100. Then create three threads, the first thread is responsible for calculating a [0] ~ a [99] This 100 elements sum　the second thread is responsible for calculating a [100] ~ a [199] This 100 elements sum　the third thread is responsible for computing a [200] ~ a [299] this is the sum of 100 elements. Finally gathered in the main function that　uates each thread, and then calculate the final result, namely a [0] ~ a sum of 300 elements [299], and print them out.