Thread: Hopelessly Lost (calling file, write to value, calculate)

this is sorta my last ditch effort here.. I have been bashing my head on the wall several days going through this.. (yes I'm rather new to C++ coding and this is what I have to do)

- have 4 files w/ information on cars (each file has 399 lines worth, x and y values)
ex. 0.967369 -19643.556725
- prompt user to pick vehicle and call the corresponding file, writing info to kw400 variable
- make sure no error opening file
- Divide Kw400 by 80000 and store the result back in Kw400
- Some of the guidance of formulas are provided..

WOW.. this doesn't feel like an intro course any longer. Just a little direction of guidance would be nice. This is supposed to be extremely basic. making user choose which model, pretty much calling a file, verify, store values in a string (don't think an array). and run a computation on results, display.

Code:

    int carNo;  // The number of the car selected

    cout << "Kw400 Crush-Work Stiffness Metric\n\n"
         << "1.  2007 Honda Civic\n"
         << "2.  2005 Chevy Cobalt\n"
         << "3.  2007 Toyota Camry\n"
         << "4.  2006 Ford Fusion\n"
         << "Choose a vehicle (1, 2, 3, 4): ";
    cin >> carNo;

    // Call the calcKw400 with one of the following filenames:
    //    honda_civic_2007.txt
    //    chevy_cobalt_2005.txt
    //    toyota_camry_2007.txt
    //    ford_fusion_2006.txt
    
// Store the result in the kw400 variable
    // Display the output with two numbers after the decimal point

    system("pause");

}

/*
 *  Function:   calcKw400
 *  Purpose:    This is function calculates the Kw400 Crush-Work
 *              Stiffness based on the values stored in the file 
 *              filename[] 
 *  Parameters: filename:  a string with the name of the file to open
 *  Returns:    the calculated Kw400 value
 */
double calcKw400(char filename[])
{
    double Kw400 = 0;
    double X = 0, Y = 0;
    double lastX = 0;
    ifstream inFile;

    // Open the file
    // Check to make sure that there was no error opening the file
    // While there is data to read in the file...
    // Divide Kw400 by 80000 and store the result back in Kw400
    // Close the file

    return Kw400;

that's very close to the basic structure I anticipated on using.. (putting it into words on this forum actually sorta got the plan more laid out in my mind)

The difficulty I'm coming into is how to pass my txt file values to the particular CalcKW400 retaining all 399 lines of information..

it is in a 0.967369 -19643.556725 line by line format.

then it must be called upon later to run a calculation of data.

Originally Posted by hk_mp5kpdw

Store the information from the file in a vector, if it's important for the two values on a single line to be "together" then your vector should contain a struct that has those two values as members:

Code:

#include <vector>
...
struct cardata
{
    double x, y;
    cardata(double x_temp = 0.0, double y_temp = 0.0) : x(x_temp), y(y_temp) {}
};
...
double calcKw400(char filename[])
{
    vector<cardata> foo;
    double tempx, tempy;

    // Open file, test for errors.
    ...

    // Load all data points from the file into the vector.
    while( inFile >> tempx >> tempy )
        foo.push_back(cardata(tempx,tempy));

    // Do something with the data in the vector, i.e. make your calculation here.
    ...

Alternately, you might just allocate a two-dimensional array of an appropriate size (2*399 elements) and stuff that with data.

I just took my exam.. so I ended up learning alot more about how it probably should be done..

the file should most likely be stored as a 2 dimensional array.
the file comparison to validate is simply a loop stating !file = etc..

everything seems to make much more sense after about 3 days of studying and reviewing all material. The basic structure of the program is still a little .. eh.. difficult to organize, at least for a beginner.

I'm trying to develop the logical flow before I devote all my time to finishing. Currently we often are voiding functions to call later. I understand the concept but it can become very confusing when there are several.

My Plan at least for flow pattern.

-Cout the user to enter the file info
-Cin their choice
-Run a switch statement to call their info
-Open the file while looping to verify correct file
-Store file in 2 dimensional array.
-Compare the values of the 2 dimensional array to determine value of Kw400
-Cout the results to user

(I'm also assuming the kw400 value should be static since per instructions state - "Divide Kw400 by 80000 and store the result back in Kw400"



thanks for the all help hk_mp5kpdw .. between full time work, MCSA classes, and a Comp Sci class.. I need all the help I can get.

Better use std::string rather than char*. This is C++, after all.