float vs string

FILE* pfi;
    char* fn = "D:/test.txt";
    pfi= fopen(fn,"w+");
    fputs("\tx=",pfi);
    fputs(x,pfi);
    fclose(pfi);

#include "stdafx.h"
#include <iostream>
using namespace std;
 
int main()
{
    FILE* pfi;
    char* fn = "D:\\test.txt";
    float x1,x2,x,h,y;
    pfi= fopen(fn,"w+");
    cout << "Enter x1: "; cin>>x1;
    cout << "Enter x2: "; cin>>x2;
    cout << "Enter  h: "; cin>>h;
    cout << "\n "<< x1 << " < x =< 3: \n"; 
    fprintf(pfi, "%.0f < x =< 3\n", x1);
    for (x = x1; x <= 3; x=x+h)
    {
        y = 1;
        for (int i=0; i<=3; i++)
        {
            y=y*(x*x+i);
        }
        fprintf(pfi, "\tx = %.1f ", x);
        fprintf(pfi, "\ty = %.2f\n", y);
        cout << "\tx= " << x << "\t y= " << y << "\n";
    }
    cout << "\n "<< x << " < x < 8: \n"; 
    fprintf(pfi, "\n%.1f < x < 8\n", x);
    for (x; x<8; x=x+h)
    {
        y = (x+2)*(x*x-3);
        fprintf(pfi, "\tx = %.1f ", x);
        fprintf(pfi, "\ty = %.2f\n", y);
        cout << "\tx= " << x << "\t y= " << y << "\n";
    }
    fclose(pfi);
    system ("pause");
}

#include "stdafx.h"
#include <Windows.h>
 
using namespace std;
 
int main(int argc, char* argv[])
{
STARTUPINFO cif;
    ZeroMemory(&cif,sizeof(STARTUPINFO));
    PROCESS_INFORMATION pi;
    CreateProcess("d:\\work.exe",NULL,
        NULL,NULL,FALSE,NULL,NULL,NULL,&cif,&pi);
}

/*
#include <fstream>
char INPUT[] = "input.txt";
char OUTPUT[] = "output.txt";
std::ifstream cin(INPUT);
std::ofstream cout(OUTPUT);
//*/

std::ifstream ifs("input.txt");
std::cin.rdbuf(ifs.rdbuf());
std::ofstream ofs("output.txt");
std::cout.rdbuf(ofs.rdbuf());

#include <fstream>
 
int main()
{
    std::streambuf* out;
    std::ofstream ofs("output.txt");
    out=std::cout.rdbuf();
    std::cout.rdbuf(ofs.rdbuf());
    std::cout<<"Someone\n";
    std::cout.rdbuf(out);
    std::cout<<"Someone\n";
    return 0;
}