main函数中结构数组a中存储了5个职员的工资信息（这里称每个职员的工资信息为一条“记录”）。sift函数的形参cond接收筛选条件字符串，函数实现从s指向数组元素开始的n个元素中筛选出所有wage符合筛选条件的记录并将这些记录复制到res指向的结构数组。函数返回res数组中存储的记录数（筛选结果）。-The main function is stored in an array of structures a five staff wages (here referred to the information of each employee s wage for a "record"). The sift function parameter cond receiver filter criteria string function to filter out all wage records match the filter conditions, and these records copied to the array of res-point structure of the n elements point to the beginning of the array elements from s. Function returns the number of records stored in the res array (screening results).