1.8

#include "stdafx.h"
#include <iostream>
#include <math.h>
#include <cmath>
using namespace std;
#define PRECISION 1e-4
double _exp(const double x)
{
    double dVal, dTemp;
    int nStep = 1;
    for (dVal = 1.0, dTemp = 1.0; fabs(dTemp) >= PRECISION; ++nStep)
    {
        dTemp *= x / nStep;
        dVal += dTemp;
    }
    return dVal;
}


int main(int argc, char** argv) {

    double x = -1;
    cout << _exp(x) << endl << exp(x) << endl;
    system("pause");
    return 0;
}