Ошибка при выводе в текстовый файл (Debug assertion failed)

#include <iostream>
#include <cmath>
#include <conio.h>
#include <stdio.h>
using namespace std;
 
bool InputCheckBool()
{//repeat input while logical constant will not be inputed
    bool logTry;
    cin >> logTry;
    while ((logTry!=0)&&(logTry!=1))
    {
        cin.clear();
        while(cin.get() != '\n');
        cout << "Incorrect answer was entered. Please, try again."<<endl;
        cin >> logTry;  
    }
    return logTry;
}
double CheckNumeric (double from, double to)
{
    double input;
    cin >> input;
    while ((input <= from)||(input >= to))
    {
        cin.clear();
        while(cin.get() != '\n');
        cout << "Incorrect answer was entered. Please, try again."<<endl;
        cin >> input;   
    }
    return input;
}
void KeyBoard(double &first, double &last, double &step, double &eror)
{
    cout <<"Enter first amount from -1 to 1 "<< endl; 
    first = CheckNumeric(-1,1);
    cout <<"Enter last amount from "<< first <<" to 1 "<< endl; 
    last = CheckNumeric(first,1);
    cout << "Input the accuracy of computing (from 0 to 1) "<< endl;
    eror = CheckNumeric(0,1);
    double diff = last - first;
    cout << "Input the step of computing (from 0 to "<< diff <<" )" << endl;
    step = CheckNumeric(0,diff);
}
void FromFile(double &first, double &last, double &step, double &eror)
{
    FILE *Input;
    char *name;
    name = new char[20];
    cout << "Please, enter file name: ";
    cin >> name;
    Input = fopen(name, "r+b");
    while (Input == NULL)
    {
        delete [] name; //here we have a problem
        cin.clear();
        while(cin.get() != '\n');
        cout << "There is not such file in the memory." << endl << "Input name: ";
        name = new char[20];
        cin >> name;
        int size = strlen(name);
        cout << size;
        Input = fopen(name, "r+b");
    }
    cout << "file was entered..."<< endl;
    fscanf(Input, "%lf %lf %lf %lf", &first, &last, &step, &eror);
    double diff = last - first;
    if ((first>last) ||  (step>diff) || (eror>1) || (eror<=0))
    {
        cout << "Data is uncorrect" << endl << "Please input numerics from keyboard" << endl;
        KeyBoard (first, last, step, eror);
    }
    else
        cout << "Data is correct" << endl;
    fclose(Input);
    delete [] name;
}
double ArcTangent (double arg, double eror)
{
double sum=0,
    element=arg;
int n=0;
 
double a,b,c;
while(abs(element)>=eror)
{
    sum += element;
    n++;
    a = -(arg*arg);
    b = (2*(n-1)+1);
    c = (2*n+1);
    element *= a*b/c;
}
return sum;
}
void Taylor(double beg, double end, double delta, double eror) 
{
    FILE *f=fopen("D:\rgr.txt", "w+b");
    double func;
    for (double argument = beg; argument <= end; argument += delta) 
    {  
         func = ArcTangent (argument,eror);
         cout <<"arctan["<< argument <<"] = "<< func << endl;
         fprintf(f, "%f\n", argument);
    } 
} 
void main (void)
{
    cout << "I will find value of arctg of any amount." << endl;
    cout << "Input:" << endl << "1 for input from keyboard" << endl << "0 for input from file" << endl;
    bool select = InputCheckBool();
    double xbegin, xend, xdelta, eror;
    bool logic = 0;
    if (select==1)
        KeyBoard(xbegin, xend, xdelta, eror);
    else
        FromFile(xbegin, xend, xdelta, eror);
    cout << "xbegin " << xbegin << endl; 
    cout << "xend " << xend << endl; 
    cout << "xdelta " << xdelta << endl; 
    cout << "eror " << eror << endl;
    Taylor(xbegin, xend, xdelta, eror);
    _getch();
}