convert string to double

[wiswis]

Hi guys. I have been looking everywhere for an answer and couldn't find one. I am a beginner in c++ and I have an assignment. The assignment asks to read a set of face values from a txt file, and depending on the face value, it will print out "doubled" ,"tripled", etc. I first defined a string face value and then i used getline to read the individual values. So far i can echo the face values just fine. My question is, how can i make a certain face value output certain things.

Here is my code:

 #include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <iomanip>
using namespace std;

void main()
{
    string sfacevalue, BonusAction;                        //define variables
    double dfacevalue = 0;

    ifstream infile;                                       //open data file
    infile.open("C++ Data File.txt");
    if (!infile)                                           //if data file doesnt exist,     print "No Data File"
        cout << "No data file!" << endl;
    cout << "Face value" << endl;

    while (infile)                                         // gets all the lines in that data file
    {
        getline(infile, sfacevalue);                       // saves the line in sfacevalue
        cout << sfacevalue << endl;                        // prints facevalue
    }

    sfacevalue = dfacevalue;                               //converts from string to double

    if (dfacevalue <= 0.35)                                //calculations
        BonusAction = "tripled";
    else if (dfacevalue > 0.35 || dfacevalue < 0.51)
        BonusAction = "doubled";
    else if (dfacevalue >= 0.51 || dfacevalue < 1.00)
        BonusAction = "value increased";


    while (dfacevalue)
    {
        cout << dfacevalue;
    }




    system("pause");
}

And here is how the output should look:


Face value Bonus action Actual value

0.49 doubled $0.98
0.28 tripled $0.84
0.74 value increased $1.00
0.34 tripled $1.02
0.50 doubled $1.00

[anup30]

   ifstream infile; 
   infile.open("C++ Data File.txt");

  double d;
  infile >> d;
  cout << 2*d;