ExpressionCalc.cpp

/*****************************************************************

    Calculation of the value of the expression. 
    Uses recursive descent parser. Supports doubles.

    Available operations: 
    + - / *     Usual meaning
    -           Unary minus
    #           Root (3 # 8 = 2)
    ^           Power (2 ^ 3 = 8)
    #           Square root (unary)

    TODO: find a good problem on it

*****************************************************************/

#include <iostream>
#include <fstream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <cstdlib>
#include <cstdio>
#include <string>
#include <utility>
#include <iomanip>

using namespace std;

string s;
int len;
double ans;
int p;

double exp();
double term();
double interm();
double factor();

double pr1Sign(char c) {
    return (c == '-' || c == '+');
}

double pr2Sign(char c) {
    return (c == '*' || c == '/');
}

double pr3Sign(char c) {
    return (c == '#' || c == '^');
}

double factor() {
    double res = 0.0, dpow = 1.0;
    bool dot = false;
    if (p >= len) {
        return res;
    }
    if (s[p] == '(') {
        p++;
        res = exp();
        p++;
        return res;
    }
    if (s[p] == '-') {
        p++;
        res = interm();
        return -res;
    }
    if (s[p] == '#') {
        p++;
        res = interm(); 
        return pow(res, 0.5);
    }
    while (p < len && ((s[p] >= '0' && s[p] <= '9') || s[p] == '.')) {
        if (s[p] == '.') 
            dot = true;
        else {
            res = res * 10 + s[p] - '0';
            if (dot) 
                dpow *= 10.0;
        }
        p++;
    }
    return res / dpow;
}

double interm() {
    double res, t;
    char c;
    res = factor();
    while (p < len && pr3Sign(s[p])) {
        c = s[p];
        p++;
        t = factor();
        if (c == '^') {
            if (t < 1.0 && t > -1.0 && t != 0 && res < 0)
                res = -pow(-res, t);
            else
                res = pow(res, t);
        }
        if (c == '#') {
            if (t < 0) 
                res = -pow(-t, (1.0 / res));
            else
                res = pow(t, (1.0 / res));
        }
    }
    return res; 
}

double term() {
    double res, t;
    char c;
    res = interm();
    while (p < len && pr2Sign(s[p])) {
        c = s[p];
        p++;
        t = interm();
        if (c == '*') 
            res *= t;
        if (c == '/') 
            res /= t;
    }
    return res;     
}

double exp() {
    double res, t;
    char c;
    res = term();
    while (p < len && pr1Sign(s[p])) {
        c = s[p];
        p++;
        t = term();
        if (c == '-') 
            res -= t;
        if (c == '+')
            res += t;
    }
    return res;
}

void remove_whitespaces(string &s) {
    string temp = s;
    s = "";

    for (int i = 0; i < (int) temp.length(); i++)
        if (temp[i] != ' ')
            s.append(1, temp[i]);
}

int main() {
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);

    getline(cin,s);
    remove_whitespaces(s);

    len = s.length();

    ans = exp();
    printf("%lg",ans);

    return 0;
}