in C++ using visual studio how can I create 3 functions one to read a file, one to sort a file, and one to output the sorted file?

Question

I'm trying to finish an assignment. which is a program that reads sales data from a text file, sorts the data and outputs the sorted data to a second file. The input file is a comma-seperated value file (CSV), with the first item being the number of sales data items to be processed, followed by the list of sales data on one line (items are seperated by commas). Each sales data item is decimal number. but I have to do this in 4 functions including the main() and that's where I'm having the most issues

Sample Input:

5,453.67,8769.57,221.87,600.28,8123.00

I'm confused on how reading in a file works and out put the data sorted.

int main() {
string filename, newFilename;
ifstream infile("salesData.csv");
//cout << "What file do you want to open? " << endl;
//cin >> filename;
int size = 0;

getSalesData(size, filename);
selectionSortArray(filename, size);
ofstream outputFile;
writeTofile(outputFile, filename);

system("pause");

return 0;
}


double * getSalesData(int &size, string &filename)
{
    ifstream inputfile;
    inputfile.open(filename);
    double * salesData = new double[size];
    inputfile.close();
    return salesData;

}

//******************************************************************
// selectionSortArray
// task: to sort values of an array in ascending order // data in: the array, the array size // data out: the sorted array
//******************************************************************
void selectionSortArray(string &filename, int length){}


// copy data to output file 
void writeTofile(ofstream &outputFile, string x)
{

    outputFile.open(x.c_str());


    outputFile.close();
}

I expect to see the sample input 5,453.67,8769.57,221.87,600.28,8123.00 to be sorted

Answer 1

I'll just deal with your main issue. You're clearly struggling with the concepts of passing parameters to functions, and returning values from functions.

Your getSalesData function is good, in that it returns the sales data but what you've missed out is that you should catch that returned value in a variable in main. Like this

int main() {
    ...
    int size = 0;
    double* salesData = getSalesData(size, filename);
    ...
}

double * getSalesData(int &size, string &filename)
{
    ...
    return salesData;
}

Once you've captured the return value you can pass it as a parameter to your other functions, e.g.

selectionSortArray(salesData, size);
writeTofile(filename, salesData, size);

Notice that you don't need to pass a file name to the sorting function, and I've just passed the file name (and not the ofstream) to the writing function. The ofstream is only needed in the writing function, so there's no need to declare it in the main function.

Every function you write, think what does this function need as parameters, and what does it return as results. Then declare that function with only those things. Variables that a function needs internally, should be declared in the function itself.

Finally your code is missing some function protoypes, normally you put these at the top of your code. Like this

double * getSalesData(int &size, string &filename);
double * selectionSortArray(double* salesData, int size);
void writeTofile(string& filename, double* salesData, int size);

This avoids any errors you might get about undeclared functions.