# hiho week 169 simple calculator

Keywords: Java Python

Time limit: 10000ms
Single point time limit: 1000ms
Memory limit: 256MB

### describe

Writing a program can complete the basic four operations with brackets. Where division (/) is an integral division and is rounded to 0 when dividing by a negative number. (the default division of C/C++/Java is to round to 0, and the default division of python is to round to negative infinity. )

For example, calculate 100 * (2 + 12) - (20 / 3) * 2, and the result is 1388.

### input

A string of no more than 100 in length, representing the calculation to be calculated. Contains the numbers 0-9 and + - * / ().

The input ensures that the calculation process will not exceed 32-bit signed integers, and the '-' in them are all minus signs without negative signs.

### output

Calculated results.

sample input
`100*(2+12)-(20/3)*2`
sample output
`1388`
Idea: mainly using the idea of stack, first convert the infix expression to suffix expression, and then calculate according to the calculation rules of suffix expression.

I think this topic is quite difficult. I couldn't start at first. After a day of careful deliberation, I finally wrote the AC code. I'm too weak for chicken. The AC code is as follows:

```#include<cstdio>
#include<cmath>
#include<iostream>
#include<string>
#include<stack>
#include<cstring>
#include<algorithm>
using namespace std;
string str;//Input string
stack<char>st;
stack<int>mp;
char s[100000];//Character array to record suffix expression
int cal(int a,int b,char op)
{
switch(op)
{
case '+':return a+b;
case '-':return a-b;
case '*':return a*b;
case '/':return a/b;
}
}
int main()
{
cin>>str;
int n=str.size();
int k=1,t=0;
while(!st.empty()) st.pop();
for(int i=0;i<100000;i++) s[i]=' ';
for(int i=0;i<n;i++)
{
if(str[i]>='0' && str[i]<='9') s[k++]=str[i];
else if(st.size()==0 && (str[i]<'0' || str[i]>'9'))//Pay attention to the order of each else if below. I can't mess it up at will. I changed it many times before I got it right
{
k++;
st.push(str[i]);
k++;
}
else if(str[i]=='(')
{
k++;
st.push(str[i]);
k++;
}
else if(str[i]==')')
{
k++;
while(st.top()!='(')
{
s[k++]=st.top();
k++;
st.pop();
}
st.pop();
}
else if(st.top()=='(')
{
k++;
st.push(str[i]);
k++;
}
else if((st.top()=='+' || st.top()=='-') && (str[i]=='*' || str[i]=='/'))
{
k++;
st.push(str[i]);
k++;
}
else if((st.top()=='*' || st.top()=='/') && (str[i]=='+' || str[i]=='-'))
{
k++;
s[k++]=st.top();
st.pop();
k++;
if(st.size()>0 && st.top()=='-')
{
s[k++]=st.top();
st.pop();
}
st.push(str[i]);
k++;
}
else if((str[i]=='*' && (st.top()=='/' || st.top()=='*')) || (str[i]=='/' && (st.top()=='*' || st.top()=='/')))
{
k++;
s[k++]=st.top();
st.pop();
st.push(str[i]);
k++;
}
else if((str[i]=='+' && (st.top()=='-' || st.top()=='+')) || (str[i]=='-' && (st.top()=='+' || st.top()=='-')))
{
k++;
s[k++]=st.top();
st.pop();
st.push(str[i]);
k++;
}
}
while(st.size()>0)
{
k++;
s[k++]=st.top();
st.pop();
}
while(!mp.empty()) mp.pop();
t=0;
for(int i=0;i<=k;i++)
{
if(s[i]=='+' || s[i]=='-' || s[i]=='*' || s[i]=='/')
{
int b=mp.top();
mp.pop();
int a=mp.top();
mp.pop();
mp.push(cal(a,b,s[i]));
}
else if(s[i]>='0' && s[i]<='9')
{
t=t*10+(s[i]-'0');
if(s[i+1]<'0' || s[i+1]>'9')
{
mp.push(t);
t=0;
}
}
}
cout<<mp.top()<<endl;
return 0;
}
//((((2+12)*3)+4)-61)+85     12-9+8*6/2-7     (9+8*5-7-8+20*3)-65+100/2    (1)+(1+2)+2*(1+3) ```

Posted by zander213 on Sat, 02 May 2020 04:09:10 -0700