Prefixes, suffixes expression evaluation

Prefix expression

Expression from right to left scanning, while a numeral, the number onto the stack, the face of the operator, the pop-up stack of two numbers, using operators calculated accordingly (the top element of the op-top element thereof ), and the result stack; repeat the process until the leftmost expression, is the value obtained by the last calculation result of the expression

From right to left, the number of pressure case 1, case 2 breaks shells, again calculated.

Postfix expression

Expression scan from left to right, when a numeral, the number onto the stack, the face of the operator, the pop-up stack of two numbers, using operators calculated accordingly (the top element of the op-top element thereof ), and the result stack; repeat the process until the leftmost expression, is the value obtained by the last calculation result of the expression

From left to right, the number of pressure case 1, case 2 breaks shells, again calculated.

example

https://www.luogu.org/problem/P1449

#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;
int a[1005],p,top,t;
char c;

int main()
{
    while(c=getchar())
    {
        if(c=='@')
            break;
        if(isdigit(c)) t=t*10+c-'0';
        if(c=='.')
        {
            a[++top]=t;
            t=0;
        }
        if(c=='+')
        {
            a[top-1]=a[top]+a[top-1];
            top--;
        }
        if(c=='-')
        {
            a[top-1]=a[top-1]-a[top];
            top--;
        }
        if(c=='*')
        {
            a[top-1]=a[top]*a[top-1];
            top--;
        }
        if(c=='/')
        {
            a[top-1]=a[top-1]/a[top];
            top--;
        }
    }
    cout<<a[top];
    return 0;
}

Precautions:

1. there is division, and to press the integer division in c ++

2.getchar () inside the cstdio