简单的中缀表达式转后缀及计算

参考着做了一下,没有检查输入是否正确,其他应该都差不多了,

为了存下浮点数,因此用了string数组,导致增加了一些类型转换函数,最后的结果也只有五位小数了,暂时懒得去想了。

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#include <iostream>
#include <string>
#include <stack>
#include <vector>

using namespace std;
int pri(char x)
{
if(x=='/' || x=='*')
return 2;
if(x=='+' || x=='-')
return 1;
if(x=='(')
return 0;
else
return -1;
}
vector<string> in_to_post(string input)
{
stack<char> s;
vector<string> post;
string t="";
int i=0;
while(input[i])
{
char tmp = (char)input[i];
if(tmp >= '0' && tmp <= '9')
{

string num_tmp;
int j = i;
while((tmp >= '0' && tmp <= '9') || tmp == '.')
{
num_tmp += tmp;
tmp = (char)input[++j];
}
post.push_back(num_tmp);
i = j-1;
}
else
{

if(s.empty())
{
s.push(tmp);
}
else if(tmp=='(')
{
s.push(tmp);
}
else if(tmp==')')
{
while(s.top()!='(')
{
t = "";
t += s.top();
post.push_back(t);
s.pop();
}
s.pop();
}
else
{
while(pri(tmp)<=pri(s.top()))
{
t = "";
t += s.top();
post.push_back(t);
s.pop();
if(s.empty())
break;
}
s.push(tmp);
}
}
i++;
}
if(!s.empty())
{
t = "";
t += s.top();
post.push_back(t);
s.pop();
}
return post;
}
double cal(double a,double b,char c)
{
if(c=='+')
return a+b;
else if(c=='-')
return a-b;
else if(c=='*')
return a*b;
else if(c=='/')
return a/b;
else
return 0;
}
int myisdigit(string s)
{
int i=0;
while(i<s.size())
{
if(s[i]!='.'&&(s[i]<'0'||s[i]>'9'))
return 0;
i++;
}
return 1;
}
double postcal(vector<string> in)
{
stack<string> s;
int i=0;
while(i<in.size())
{
string tmp = in[i];
if(myisdigit(tmp))
{
s.push(tmp);
}
else
{
double b = stod(s.top());
s.pop();
double a= stod(s.top());
s.pop();
char c = tmp[0];
double r = cal(a,b,c);
s.push(to_string(r));
}
i++;
}
return stod(s.top());
}
int main()
{
string input;
int i=0;
vector<string> postinput;
cout<<"请输入中缀表达式:"<<endl;
cin>>input;

postinput=in_to_post(input);
cout<<"后缀表达式为:"<<endl;
for(i=0; i<postinput.size(); i++)
{
cout<<postinput[i]<<" ";
}

double res = postcal(postinput);

cout<<endl<<"结果为:"<<res<<endl;

return 0;
}
/*
请输入中缀表达式:
1.2*((2/4.3)*3.2)
后缀表达式为:
1.2 2 4.3 / 3.2 * *
结果为:1.78605

to_string stod均为c++11特性,需编译器支持,
in codeblocks,go to settings->compiler->check the "have g++ follow the c++11 ISO..."
*/