中缀表达式直接计算(带括号)
#include<bits/stdc++.h>
using namespace std;
//中缀表达式求值
string mid;
stack<double> data_stack;
stack<char> op_stack;
int Priority(char op){
if(op=='+'||op=='-') return 1;
else if(op=='*'||op=='/') return 2;
else if(op=='(') return 0;//注意
}
double Calculate(double a,double b,char op){
if(op=='+') return a+b;
else if(op=='-') return a-b;
else if(op=='*') return a*b;
else if(op=='/') return a/b;
}
double getNumber(string str,int& pos){//pos是共享的
double ans=0.0;
while(isdigit(str[pos])){
ans=ans*10+(double)(str[pos++]-'0');
}
pos--;
return ans;
}
//1+2*3
int main(){
cin>>mid;
for(int i=0;i<mid.size();i++){
if(isdigit(mid[i])){
//cout<<(double)(mid[i]-'0')<<endl;
//cout<<"data "<<data_stack.size()<<endl;
double number=getNumber(mid,i);
//cout<<"数字:"<<number<<endl;
data_stack.push(number);
}
else if(mid[i]=='('){
op_stack.push(mid[i]);
}
else if(mid[i]==')'){
while(op_stack.top()!='('){
char op=op_stack.top(); op_stack.pop();
double b=data_stack.top(); data_stack.pop();
double a=data_stack.top(); data_stack.pop();
double temp=Calculate(a,b,op);
data_stack.push(temp);
}
op_stack.pop();
}
else{
//cout<<"op "<<mid[i]<<endl;
while((!op_stack.empty())&&Priority(op_stack.top())>=Priority(mid[i])){//顺序不能变，一定是先判栈空
char op=op_stack.top(); op_stack.pop();
double b=data_stack.top(); data_stack.pop();
double a=data_stack.top(); data_stack.pop();
double temp=Calculate(a,b,op);
//cout<<a<<op<<b<<"结果"<<temp<<endl;
data_stack.push(temp);
}
op_stack.push(mid[i]);
}
}
while(!op_stack.empty()){//别忘了将op清空
char op=op_stack.top(); op_stack.pop();
double b=data_stack.top(); data_stack.pop();
double a=data_stack.top(); data_stack.pop();
double temp=Calculate(a,b,op);
data_stack.push(temp);
}
cout<<data_stack.top()<<endl;
}
中缀转后缀与后缀表达式计算(带括号)
PS:后缀表达式中两两之间一定要用空格隔开，不然getNumber函数就不起作用了
#include<bits/stdc++.h>
using namespace std;
//中缀转后缀+后缀求值
string post="",mid;
stack<char> op_stack;
stack<double> data_stack;
int Priority(char op){
if(op=='+'||op=='-') return 1;
else if(op=='*'||op=='/') return 2;
else if(op=='(') return 0;
}
double Calculate(double a,double b,char op){
if(op=='+') return a+b;
else if(op=='-') return a-b;
else if(op=='*') return a*b;
else if(op=='/') return a/b;
}
double getNumber(string str,int& pos){//pos是共享的
double ans=0.0;
while(isdigit(str[pos])){
ans=ans*10+(double)(str[pos++]-'0');
}
pos--;//不然会越过一个位置
return ans;
}
//9+(3-1)*3+10/2，转换的话不会用到getnumber得到多位的整数
void Transform(){
for(int i=0;i<mid.size();i++){
//cout<<post<<endl;
if(isdigit(mid[i])){//这里得到完整数直接写就行!!!
while(isdigit(mid[i])){
post=post+mid[i++];
}
i--;//不然会把下一个覆盖掉
post=post+" ";
}
else if(mid[i]==' '){
continue;
}
else if(mid[i]=='('){
op_stack.push(mid[i]);
}
else if(mid[i]==')'){
while(op_stack.top()!='('){
char op=op_stack.top();
op_stack.pop();
post=post+op+" ";
}
op_stack.pop();//将'('pop出来
}
else{//为操作符
//cout<<"操作符 "<<mid[i]<<endl;
if(op_stack.empty()){
op_stack.push(mid[i]);
continue;
}
else{
//别忘了判栈空
while(!op_stack.empty()&&Priority(op_stack.top())>=Priority(mid[i])){
//cout<<op_stack.top()<<"pop 出来"<<endl;
char op=op_stack.top();
op_stack.pop();
post=post+op+" ";
}
op_stack.push(mid[i]);
}
}
}
while(!op_stack.empty()){
char op=op_stack.top();
op_stack.pop();
post=post+op;
}
}
int main(){
cin>>mid;
Transform();
cout<<"后缀表达式:"<<post<<endl;
for(int pos=0;pos<post.size();pos++){
if(isdigit(post[pos])){
double number=getNumber(post,pos);
//cout<<"数字:"<<number;
data_stack.push(number);
}
else if(post[pos]==' ') continue;
else{
char op=post[pos];
double b=data_stack.top(); data_stack.pop();
double a=data_stack.top(); data_stack.pop();
double temp=Calculate(a,b,op);
//cout<<"运算后 "<<temp<<endl;
data_stack.push(temp);
}
}
cout<<"运算结果:"<<data_stack.top()<<endl;
}