#include "Calculator.h"
#include<stdlib.h>

Calculator::Calculator(string & str) :str(str),cur(0),ans(0)
{
    ans = expression();
}

Calculator::~Calculator()
{
}

double Calculator::expression()
{
    double num1 = term();
    double num2;
    while (str[cur] == '+' || str[cur] == '-')
    {
        char op = str[cur++];    //運算符
        num2 = term();
        if (op == '+')    num1 += num2;
        else if (op == '-')    num1 -= num2;
    }
    if (str[cur] == ')')    ++cur;    //factor遇到'('會調用此函數，因此要吃掉')'
    return num1;
}

double Calculator::term()
{
    double num1 = factor();
    double num2;
    while (str[cur] == '*' || str[cur] == '/')
    {
        char op = str[cur++] ;
        num2 = factor();
        if (op == '*')    num1 *= num2;
        else if (op == '/')    num1 /= num2;
    }
    return num1;
}

double Calculator::factor()
{
    char tmp = str[cur];
    double result = tmp - '0';
    ++cur;
    if (tmp == '(')
        return expression();
    else
    {//取數字
        int flag = 0;//0為小數點之前，1位小數點之后
        double temp = 10;
        while (str[cur] >= '0' && str[cur] <= '9' || str[cur]=='.')
        {
            if (str[cur] == '.')
            {
                ++cur;
                flag = 1;
            }
            else
            {
                if (!flag)//小數點之前
                    result = result * 10 + str[cur] - '0';
                else
                {
                    result = result + double(str[cur] - '0') / temp;
                    temp *= 10;
                }
                ++cur;
            }
        }        
        return result;
    }
}