C++二叉树应用：计算算术表达式

本文转自：http://www.duote.com/tech/5/14777.html

#include<iostream>using namespace std;class calc{enum Type{DATA,ADD,SUB,MULTI,DIV,OPAREN,CPAREN,EOL};struct node{Type type;int data;node *lchild,*rchild;node(Type t,int d=0,node*lc=NULL,node *rc=NULL){type=t;data=d;lchild=lc;rchild=rc;}};node *root;node *create(char *&s);Type getToken(char *&s,int &value);int result (node *t);public:calc(char *s){root=create(s);}int result(){if(root==NULL)return 0;return result(root);}};calc::node *calc::create(char *&s){//((2+3*2)-(12-6))/2=1node *p,*root=NULL;Type returnType=DATA;Type flag=DATA;int value;while(*s){flag=returnType;returnType=getToken(s,value);switch(returnType){case DATA:case OPAREN:if(returnType==DATA)p=new node(DATA,value);else p=create(s);if(root==NULL)root=p;else if(root->rchild==NULL)root->rchild=p;else root->rchild->rchild=p;break;case CPAREN:case EOL:return root;case ADD:case SUB:root=new node(returnType,0,root);break;case MULTI:case DIV:if(root->type==DATA||root->type==MULTI||root->type==DIV||flag==OPAREN)root=new node(returnType,0,root);else root->rchild=new node(returnType,0,root->rchild);}}return root;}calc::Type calc::getToken(char *&s,int &data){char type;while(*s==' ')++s;if(*s>='0'&&*s<='9'){data=0;while(*s>='0'&&*s<='9'){data=data*10+*s-'0';++s;}return DATA;}if(*s=='\0')return EOL;type=*s;++s;switch(type){case '+':return ADD;case '-':return SUB;case '*':return MULTI;case '/':return DIV;case '(':return OPAREN;case ')':return CPAREN;default:return EOL;}}int calc::result(node*t){int num1,num2;if(t->type==DATA)return t->data;num1=result(t->lchild);num2=result(t->rchild);switch(t->type){case ADD:t->data=num1+num2;break;case SUB:t->data=num1-num2;break;case MULTI:t->data=num1*num2;break;case DIV:t->data=num1/num2;break;}return t->data;}int main(){char equation[256];cin>>equation;//calc exp("3*(2+(6/2))");calc exp(equation);cout<<exp.result()<<endl;return 0;}

运行结果：输入算术表达式，按Enter键即可。