iteration_stmt(void);Р?TreeNode * return_stmt(void);Р?TreeNode * expression(void);Р?TreeNode * var(void);Р?TreeNode * simple_expression(TreeNode * k);Р?TreeNode * additive_expression(TreeNode * k);Р?TreeNode * term(TreeNode * k);Р?TreeNode * factor(TreeNode * k);?Р?TreeNode * call(TreeNode * k);Р?TreeNode * args(void);Р2.1.4 测试程序说明Р根据附录A后面的例子,程序输入两个整数,计算并打印出它们的最大公因子,保存为a.txt。Р/* A program to perform Eucild'sР Algorithm pute gcd. */Рint gcd (int u, int v)Р{Р if (v==0) Р return u;Р else return Р gcd(v,u-u/v*v); /* u-u/v*v== u mod v */Р}Рvoid main(void)Р{Р int x;Р int y;Р x=input(); Р y=input();Р output(gcd(x,y));Р}Р程序代码实现Р按文件列出主要程序代码, 添加必要的注释.РScanner.cpp:Р#include <cstdlib>Р#include <iostream>Р#include <fstream>Р#include <string>Р#include "scanner.h"Р#include<vector>Рusing namespace std;Р/*